<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019dd587-38d4-7ace-9da0-7ba68cab512f,g:94e804ce-26ea-4287-a031-aed431bde722-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.dpandl.com/role/CoverStatement" xlink:type="simple" xlink:href="dpl-20260331.xsd#CoverStatement"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CoverStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3a58-7892-9545-382b6aada49b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntitiesTable_019dd587-3a58-7892-9545-382b6aada49b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e21-b8e1-7b702486a6c6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3a58-7892-9545-382b6aada49b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e21-b8e1-7b702486a6c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7e21-b8e1-7b702486a6c6_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e21-b8e1-7b702486a6c6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7e21-b8e1-7b702486a6c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7965-856c-310130b0497c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e21-b8e1-7b702486a6c6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7965-856c-310130b0497c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-78b2-b3d0-7e89775d8b0c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7965-856c-310130b0497c" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-78b2-b3d0-7e89775d8b0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019dd587-3a58-7889-b71b-80763f1c0399" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentFiscalYearFocus_019dd587-3a58-7889-b71b-80763f1c0399" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019dd587-3a58-7872-93f4-771e314420f5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019dd587-3a58-7872-93f4-771e314420f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019dd587-3a58-7d89-88f9-a30131db84ee" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityCentralIndexKey_019dd587-3a58-7d89-88f9-a30131db84ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019dd587-3a58-79c5-86fd-fa1c380a1ea5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_CurrentFiscalYearEndDate_019dd587-3a58-79c5-86fd-fa1c380a1ea5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019dd587-3a58-72f5-be9a-2dbb05096faf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_AmendmentFlag_019dd587-3a58-72f5-be9a-2dbb05096faf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019dd587-3a58-7529-918b-bf1e19c95c50" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityCurrentReportingStatus_019dd587-3a58-7529-918b-bf1e19c95c50" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019dd587-3a58-7c38-81aa-4cdae57b867f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentType_019dd587-3a58-7c38-81aa-4cdae57b867f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019dd587-3a58-793a-b49f-66865eb99d2a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentQuarterlyReport_019dd587-3a58-793a-b49f-66865eb99d2a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019dd587-3a58-7f32-80ef-510fe6e1818f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityInteractiveDataCurrent_019dd587-3a58-7f32-80ef-510fe6e1818f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019dd587-3a58-7366-ad1a-8132c0e23cb4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityFilerCategory_019dd587-3a58-7366-ad1a-8132c0e23cb4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019dd587-3a58-74c6-9949-e859913504a2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityShellCompany_019dd587-3a58-74c6-9949-e859913504a2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019dd587-3a58-762b-9dc0-3b2b46661f59" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentPeriodEndDate_019dd587-3a58-762b-9dc0-3b2b46661f59" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019dd587-3a58-756d-bee9-b128057ee34d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_DocumentTransitionReport_019dd587-3a58-756d-bee9-b128057ee34d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019dd587-3a58-7b1a-824d-ad14f2b6cdd5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityRegistrantName_019dd587-3a58-7b1a-824d-ad14f2b6cdd5" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019dd587-3a58-72d5-abf7-5a51ec4ce4f2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019dd587-3a58-72d5-abf7-5a51ec4ce4f2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019dd587-3a58-78c9-8568-733305cfd5b6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityFileNumber_019dd587-3a58-78c9-8568-733305cfd5b6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019dd587-3a58-7de9-92ab-46361e2ff98e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityAddressAddressLine1_019dd587-3a58-7de9-92ab-46361e2ff98e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019dd587-3a58-7196-8260-2604268bfb10" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityAddressPostalZipCode_019dd587-3a58-7196-8260-2604268bfb10" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019dd587-3a58-7334-a90d-1845843cb358" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_LocalPhoneNumber_019dd587-3a58-7334-a90d-1845843cb358" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019dd587-3a58-7c04-a134-69a5dc5d6ca7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityTaxIdentificationNumber_019dd587-3a58-7c04-a134-69a5dc5d6ca7" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019dd587-3a58-7505-810f-6985c5a1bfc3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntitySmallBusiness_019dd587-3a58-7505-810f-6985c5a1bfc3" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019dd587-3a58-7777-ae31-608e04d6f842" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityEmergingGrowthCompany_019dd587-3a58-7777-ae31-608e04d6f842" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019dd587-3a58-7324-85c1-0ea451b89851" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019dd587-3a58-7324-85c1-0ea451b89851" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019dd587-3a58-785f-a374-37fba1afc990" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityAddressCityOrTown_019dd587-3a58-785f-a374-37fba1afc990" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019dd587-3a58-7744-89a9-45cebd4d3e25" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_EntityAddressStateOrProvince_019dd587-3a58-7744-89a9-45cebd4d3e25" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019dd587-3a58-73a1-a646-513d0a21184a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3a58-7ae5-bb81-c974c414d284" xlink:to="loc_dei_CityAreaCode_019dd587-3a58-73a1-a646-513d0a21184a" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019dd587-3a58-730d-8759-23bacfd3558e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019dd587-3a58-7608-814e-bb38d60f4a43" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019dd587-3a58-730d-8759-23bacfd3558e" xlink:to="loc_dei_DocumentInformationTable_019dd587-3a58-7608-814e-bb38d60f4a43" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019dd587-3a58-7eba-9e04-f4a9db6363be" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dd587-3a58-730d-8759-23bacfd3558e" xlink:to="loc_dei_EntityCurrentReportingStatus_019dd587-3a58-7eba-9e04-f4a9db6363be" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-717b-8e62-11f9052f60d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-717b-8e62-11f9052f60d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f31-a563-90977c9df8f3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-717b-8e62-11f9052f60d5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f31-a563-90977c9df8f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7f31-a563-90977c9df8f3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f31-a563-90977c9df8f3" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7f31-a563-90977c9df8f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7117-9374-5ac858421a23" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f31-a563-90977c9df8f3" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7117-9374-5ac858421a23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-7816-bafc-7a0e502d28c6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7117-9374-5ac858421a23" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-7816-bafc-7a0e502d28c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-3a58-799b-9214-92ab46087870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_Revenues_019dd587-3a58-799b-9214-92ab46087870" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-3a58-7427-9d3b-8745c6ffeef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpensePurchasedPower"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-3a58-7427-9d3b-8745c6ffeef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-3a58-769d-9810-80cf5431a036" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-3a58-769d-9810-80cf5431a036" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-3a58-7349-863c-f559c011aa78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-3a58-7349-863c-f559c011aa78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-3a58-7796-80d2-314501355756" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-3a58-7796-80d2-314501355756" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_019dd587-3a58-7f2a-b444-6d6dc882acfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019dd587-3a58-7002-aa76-c9eda3d6f47a" xlink:to="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_019dd587-3a58-7f2a-b444-6d6dc882acfc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019dd587-3a58-76ed-a45b-d9e470ce92c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_CostsAndExpenses_019dd587-3a58-76ed-a45b-d9e470ce92c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019dd587-3a58-7de1-8c72-f0bfba7d11a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_OperatingIncomeLoss_019dd587-3a58-7de1-8c72-f0bfba7d11a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-3a58-76e3-ae4c-16156b34b3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-3a58-76e3-ae4c-16156b34b3ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-3a58-77d1-8137-478ec5c80d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-3a58-77d1-8137-478ec5c80d4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dd587-3a58-7868-a967-5e8f3f2b37ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dd587-3a58-7868-a967-5e8f3f2b37ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-3a58-740b-a04e-8ae7e52470c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019dd587-3a58-7c84-817c-2dc8a680d282" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-3a58-740b-a04e-8ae7e52470c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3a58-783d-82e9-c064d410d06d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3a58-783d-82e9-c064d410d06d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3a58-73bd-810e-aff9ad3d0976" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3a58-73bd-810e-aff9ad3d0976" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-736c-89b3-8918ee7fb369" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-736c-89b3-8918ee7fb369" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-3a58-7881-90ab-9051d3830c9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-3a58-7881-90ab-9051d3830c9d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3a58-7841-ba92-6c088c7a7998" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7388-8aa3-3c234fdf24f9" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3a58-7841-ba92-6c088c7a7998" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7657-8e01-2211e3d6af9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7657-8e01-2211e3d6af9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7657-8e01-2211e3d6af9c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7657-8e01-2211e3d6af9c" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7657-8e01-2211e3d6af9c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7540-8da7-4e881cd6a251" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7657-8e01-2211e3d6af9c" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7540-8da7-4e881cd6a251" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019dd587-3a58-7304-8e16-28c8fd076ebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7540-8da7-4e881cd6a251" xlink:to="loc_us-gaap_RetainedEarningsMember_019dd587-3a58-7304-8e16-28c8fd076ebe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3a58-7b17-82c5-9b55fd77b6fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7540-8da7-4e881cd6a251" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3a58-7b17-82c5-9b55fd77b6fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3a58-7fba-82ea-4bb134676654" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7540-8da7-4e881cd6a251" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3a58-7fba-82ea-4bb134676654" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e64-b924-4851f2fbd09b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e64-b924-4851f2fbd09b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7e64-b924-4851f2fbd09b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e64-b924-4851f2fbd09b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7e64-b924-4851f2fbd09b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7d31-9d9c-c757e1758791" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7e64-b924-4851f2fbd09b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7d31-9d9c-c757e1758791" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-7d92-a4a4-58b7535bb49e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7d31-9d9c-c757e1758791" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-7d92-a4a4-58b7535bb49e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7cc2-a05b-4296566e5fee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7cc2-a05b-4296566e5fee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7cc2-a05b-4296566e5fee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7cc2-a05b-4296566e5fee" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7cc2-a05b-4296566e5fee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7cab-af0d-30a40943aa1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7cc2-a05b-4296566e5fee" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7cab-af0d-30a40943aa1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-7619-a328-469e62ecedc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7cab-af0d-30a40943aa1d" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-7619-a328-469e62ecedc6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-745c-85dc-e2e9472db596" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7db3-832c-411855a826f1" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-745c-85dc-e2e9472db596" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-745c-85dc-e2e9472db596_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-745c-85dc-e2e9472db596" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-745c-85dc-e2e9472db596_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7cdb-83c7-836ca5aaeb3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-745c-85dc-e2e9472db596" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7cdb-83c7-836ca5aaeb3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3a58-7c04-ad92-9a08c65ead8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7cdb-83c7-836ca5aaeb3b" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-3a58-7c04-ad92-9a08c65ead8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3a58-777f-8734-db7e3a3867fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3a58-777f-8734-db7e3a3867fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7535-b1c4-2cc336060ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7535-b1c4-2cc336060ccf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-71a9-827c-900d61b9f9b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7535-b1c4-2cc336060ccf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-71a9-827c-900d61b9f9b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019dd587-3a58-774b-8840-4524fb2aed78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7535-b1c4-2cc336060ccf" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019dd587-3a58-774b-8840-4524fb2aed78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7607-ad7c-48d4136d851f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7607-ad7c-48d4136d851f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-3a58-73dd-8dee-ef918be75006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7607-ad7c-48d4136d851f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-3a58-73dd-8dee-ef918be75006" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dd587-3a58-7f6c-9f86-9e7278c6da7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7607-ad7c-48d4136d851f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dd587-3a58-7f6c-9f86-9e7278c6da7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7229-9aa0-0abea4ea48b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-3a58-7607-ad7c-48d4136d851f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7229-9aa0-0abea4ea48b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-7bd0-9f98-f9b3df3809f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7056-bcb0-88dfb4c1c9f0" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-7bd0-9f98-f9b3df3809f1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-7734-a998-c8a4fa9ed18b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-7734-a998-c8a4fa9ed18b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f6d-93b8-f77ae9267af1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7734-a998-c8a4fa9ed18b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f6d-93b8-f77ae9267af1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7f6d-93b8-f77ae9267af1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f6d-93b8-f77ae9267af1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7f6d-93b8-f77ae9267af1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-71db-8a23-71d1ba150e53" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7f6d-93b8-f77ae9267af1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-71db-8a23-71d1ba150e53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-799c-bc23-862e41986ecc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-71db-8a23-71d1ba150e53" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-799c-bc23-862e41986ecc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-3a58-7dc8-bee2-e179235c94ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-3a58-7dc8-bee2-e179235c94ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-3a58-7448-b5ce-2d39c06074c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-3a58-7448-b5ce-2d39c06074c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-78e8-9e86-fc16e9fd42d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-78e8-9e86-fc16e9fd42d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-3a58-7147-a429-823de0d219bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-3a58-7147-a429-823de0d219bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ComprehensiveIncomeAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-7c44-abbb-4bbf6650683a" xlink:href="dpl-20260331.xsd#dpl_ComprehensiveIncomeAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_dpl_ComprehensiveIncomeAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-7c44-abbb-4bbf6650683a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019dd587-3a58-7f72-a543-d4311fde9b31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019dd587-3a58-7f72-a543-d4311fde9b31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ComprehensiveIncomeAttributableToNoncontrollingInterest_019ddac7-1160-74c9-b513-0b55039fa95a" xlink:href="dpl-20260331.xsd#dpl_ComprehensiveIncomeAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_dpl_ComprehensiveIncomeAttributableToNoncontrollingInterest_019ddac7-1160-74c9-b513-0b55039fa95a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ddac8-f1f8-76e8-ad17-971b3c52e2ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ddac8-f1f8-76e8-ad17-971b3c52e2ed" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019de045-d257-7495-8d28-776e06cb0811" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7934-8417-5301319a7f54" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019de045-d257-7495-8d28-776e06cb0811" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-7b8d-8ba9-f1d8ba15150e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-7b8d-8ba9-f1d8ba15150e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7878-bc46-2e1fbafca447" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7b8d-8ba9-f1d8ba15150e" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7878-bc46-2e1fbafca447" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7878-bc46-2e1fbafca447_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7878-bc46-2e1fbafca447" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7878-bc46-2e1fbafca447_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7719-bc59-27b7e5860e2b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7878-bc46-2e1fbafca447" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7719-bc59-27b7e5860e2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-72b2-8223-ef3d1039df11" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7719-bc59-27b7e5860e2b" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-72b2-8223-ef3d1039df11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019dd587-3a58-751c-8896-82ccd17701ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_AssetsAbstract_019dd587-3a58-751c-8896-82ccd17701ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dd587-3a58-751c-8896-82ccd17701ea" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7f53-bb60-60a53d63c126" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7f53-bb60-60a53d63c126" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-7777-95ce-49b98b72428d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-7777-95ce-49b98b72428d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019dd587-3a58-7c7d-8b3f-13d8f25c4fce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_InventoryNet_019dd587-3a58-7c7d-8b3f-13d8f25c4fce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-3a58-70bf-868c-e8e361389116" xlink:href="dpl-20260331.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-3a58-70bf-868c-e8e361389116" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-3a58-75a3-b87b-60f1c6fbf768" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-3a58-75a3-b87b-60f1c6fbf768" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019dd587-3a58-7e46-a363-e264371fba5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019dd587-3a58-7e46-a363-e264371fba5f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019dd587-3a58-7374-a75f-2480389c33a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_OtherAssetsCurrent_019dd587-3a58-7374-a75f-2480389c33a9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019dd587-3a58-7344-b79f-899d57adef78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_AssetsCurrent_019dd587-3a58-7344-b79f-899d57adef78" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-70e7-a2c6-2bd184d6072f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019dd587-3a58-7c44-b584-8e8906d3a453" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-70e7-a2c6-2bd184d6072f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-3a58-78eb-a927-baeeb8ec5108" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019dd587-3a58-751c-8896-82ccd17701ea" xlink:to="loc_us-gaap_Assets_019dd587-3a58-78eb-a927-baeeb8ec5108" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_019dd587-3a58-74f5-9f41-3a29889f97de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_DebtCurrent_019dd587-3a58-74f5-9f41-3a29889f97de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dd587-3a58-77d3-a170-0c57234d96a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dd587-3a58-77d3-a170-0c57234d96a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_019dd587-3a58-7f11-bb6f-8ea67bf1e615" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_TaxesPayableCurrent_019dd587-3a58-7f11-bb6f-8ea67bf1e615" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dd587-3a58-7ce2-981d-e62df7d76baa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_InterestPayableCurrent_019dd587-3a58-7ce2-981d-e62df7d76baa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-3a58-7600-827c-418831d8a643" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-3a58-7600-827c-418831d8a643" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-3a58-7695-bfd8-3267a07f69f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-3a58-7695-bfd8-3267a07f69f9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-3a58-7f87-950c-c4631a35c834" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-3a58-7f87-950c-c4631a35c834" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dd587-3a58-7f93-9a78-d440d341d970" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-3a58-7f7c-b80e-9dda1fcacfad" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dd587-3a58-7f93-9a78-d440d341d970" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3a58-7707-b0ae-7dda487ea645" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3a58-7707-b0ae-7dda487ea645" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3a58-75b4-9d97-6c467dd09b37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3a58-75b4-9d97-6c467dd09b37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3a58-7eb6-a5e9-e4f207bd6275" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3a58-7eb6-a5e9-e4f207bd6275" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-3a58-7e23-b4cf-343463e69cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-3a58-7e23-b4cf-343463e69cb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-3a58-7931-bc50-9b0e497c5805" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-3a58-7931-bc50-9b0e497c5805" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-3a58-7552-9b41-0c6770cb707a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-3a58-7552-9b41-0c6770cb707a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_019dd587-3a58-7f2a-a2c7-c76078ec8ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-3a58-70c7-9277-25f472998179" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_019dd587-3a58-7f2a-a2c7-c76078ec8ba1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019dd587-3a58-769d-8ebd-8c1408660c48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019dd587-3a58-769d-8ebd-8c1408660c48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3a58-71df-bd10-de536b639594" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3a58-71df-bd10-de536b639594" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7da7-9ffe-9a09a372c066" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7da7-9ffe-9a09a372c066" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-3a58-72dd-bcab-64e8926d479a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:to="loc_us-gaap_CommonStockValue_019dd587-3a58-72dd-bcab-64e8926d479a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-7415-8609-b42467ffe88e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-7415-8609-b42467ffe88e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7cd0-967e-91802f7aa16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7cd0-967e-91802f7aa16e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-77ef-b39e-f0ed38818452" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-77ef-b39e-f0ed38818452" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-778f-8585-86e56a36b3c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-3a58-7ee0-8ccf-35fc8807b58b" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-778f-8585-86e56a36b3c0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dd587-3a58-7f1d-92dd-4544adfa10d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-3a58-7179-a173-0a47228d79b7" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dd587-3a58-7f1d-92dd-4544adfa10d4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dd587-3a58-7dbe-96ed-5cc3eff095b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dd587-3a58-7dbe-96ed-5cc3eff095b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-788e-b191-ea7e68477aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-788e-b191-ea7e68477aa4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019dd587-3a58-7321-b47d-b63e754b7e99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_CommonStockSharesIssued_019dd587-3a58-7321-b47d-b63e754b7e99" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dd587-3a58-7555-a453-af1a7e57918c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_Liabilities_019dd587-3a58-7555-a453-af1a7e57918c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-7e2a-a2ed-f59fc9ec69fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-7e2a-a2ed-f59fc9ec69fe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3a58-773f-aa2e-a14dead30bcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3a58-773f-aa2e-a14dead30bcc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-3a58-777e-8eb9-372f001cb7bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-3a58-777e-8eb9-372f001cb7bc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-7195-b421-3a47d17bca77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-7195-b421-3a47d17bca77" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_019dd587-3a58-7ce8-b4c5-dc70dba3dbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_AssetsNoncurrent_019dd587-3a58-7ce8-b4c5-dc70dba3dbc8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dd587-3a58-7cf4-85e3-52e2a87d7bcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-721a-9fb3-f35d7b63dbc7" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dd587-3a58-7cf4-85e3-52e2a87d7bcd" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-7ce3-a6df-77ba8c7e8960" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-7ce3-a6df-77ba8c7e8960" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7739-882c-8e07fadf44f9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7ce3-a6df-77ba8c7e8960" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7739-882c-8e07fadf44f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7739-882c-8e07fadf44f9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7739-882c-8e07fadf44f9" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7739-882c-8e07fadf44f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7681-8066-57f40061d441" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7739-882c-8e07fadf44f9" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7681-8066-57f40061d441" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-7dd6-abbb-9108d0ec0f14" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7681-8066-57f40061d441" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-7dd6-abbb-9108d0ec0f14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-78ce-83be-e528d522f981" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-78ce-83be-e528d522f981" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019dd587-3a58-713b-9828-bde318fcd332" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommonStockSharesIssued_019dd587-3a58-713b-9828-bde318fcd332" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dd587-3a58-7529-a80e-291c804f4e1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dd587-3a58-7529-a80e-291c804f4e1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7dda-89b5-c719847e3743" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7dda-89b5-c719847e3743" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-7aa5-9618-14859629330f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-7aa5-9618-14859629330f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7a6f-9fa2-93c9d2190955" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7a6f-9fa2-93c9d2190955" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7ea7-9d52-d1f528555cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7ea7-9d52-d1f528555cdb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019ddacc-b578-72d9-ab80-f94bd3cef9b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019ddacc-b578-72d9-ab80-f94bd3cef9b5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-7b68-b4d8-0cc21b88e8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-7b68-b4d8-0cc21b88e8e9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019dd587-3a58-7728-bd3f-6c407d781620" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_InventoryNet_019dd587-3a58-7728-bd3f-6c407d781620" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-3a58-707c-94ef-514378cdead0" xlink:href="dpl-20260331.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-3a58-707c-94ef-514378cdead0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-3a58-730e-8630-c01ac94050a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-3a58-730e-8630-c01ac94050a1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019dd587-3a58-70f4-9ed8-ae7af703a0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019dd587-3a58-70f4-9ed8-ae7af703a0d6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019dd587-3a58-7ccd-bd43-b6b2a1b44e6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_OtherAssetsCurrent_019dd587-3a58-7ccd-bd43-b6b2a1b44e6f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019dd587-3a58-7329-8655-e1c3027cf2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019dd587-3a58-7329-8655-e1c3027cf2a3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-787b-8618-5a0395629ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-787b-8618-5a0395629ec5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3a58-7af6-b9eb-eabfaf6eee0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3a58-7af6-b9eb-eabfaf6eee0d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-3a58-784b-b923-c5b1f5347913" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-3a58-784b-b923-c5b1f5347913" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dd587-3a58-7142-b807-dbe52c1c8d12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dd587-3a58-7142-b807-dbe52c1c8d12" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dd587-3a58-7d21-9379-2586b10c015c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dd587-3a58-7d21-9379-2586b10c015c" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_019dd587-3a58-7ecb-8921-7ff5c322d460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_DebtCurrent_019dd587-3a58-7ecb-8921-7ff5c322d460" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dd587-3a58-701d-b2de-3de254dcc987" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dd587-3a58-701d-b2de-3de254dcc987" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_019dd587-3a58-79d1-b518-6c026cdd6f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_TaxesPayableCurrent_019dd587-3a58-79d1-b518-6c026cdd6f9b" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dd587-3a58-7387-880f-62c739482764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_InterestPayableCurrent_019dd587-3a58-7387-880f-62c739482764" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-3a58-791a-a7ab-7baa2ce8cc0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-3a58-791a-a7ab-7baa2ce8cc0d" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-3a58-7b5b-86fc-d907672ab62e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-3a58-7b5b-86fc-d907672ab62e" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-3a58-7e54-b0ae-0157011def35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-3a58-7e54-b0ae-0157011def35" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3a58-73c1-a446-e51c14f03ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3a58-73c1-a446-e51c14f03ae0" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3a58-7b1c-a812-1c590250badc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3a58-7b1c-a812-1c590250badc" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3a58-73f2-a011-0c0c513c7744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3a58-73f2-a011-0c0c513c7744" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-3a58-77e3-bc8c-78e32319de0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-3a58-77e3-bc8c-78e32319de0c" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-3a58-7c74-bc1f-a3dcfa7f6185" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-3a58-7c74-bc1f-a3dcfa7f6185" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-3a58-7373-a9d6-3a9bb063fe6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-3a58-7373-a9d6-3a9bb063fe6f" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-3a58-7ce2-85ac-5d6197c35377" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommonStockValue_019dd587-3a58-7ce2-85ac-5d6197c35377" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-7ba3-b592-6176c1af4567" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-7ba3-b592-6176c1af4567" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7b2b-beea-ee1bd3b69223" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7b2b-beea-ee1bd3b69223" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-72f1-baaf-a1f1209e182b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-72f1-baaf-a1f1209e182b" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ddad0-028b-77a0-988e-993a023077fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_StockholdersEquity_019ddad0-028b-77a0-988e-993a023077fa" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dd587-3a58-77eb-898c-4ff9874782fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_Liabilities_019dd587-3a58-77eb-898c-4ff9874782fc" xlink:type="arc" order="38"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019ddad1-852f-756c-9344-a2087b2d15e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019ddad1-852f-756c-9344-a2087b2d15e3" xlink:type="arc" order="39"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-7611-98f9-4beac85dc28b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-7611-98f9-4beac85dc28b" xlink:type="arc" order="40"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_019dd587-3a58-7533-a575-fd4004549e3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_019dd587-3a58-7533-a575-fd4004549e3c" xlink:type="arc" order="41"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019de045-96cb-7b17-953e-1b54d7a8a0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-74f8-a67f-38a70f2d0ba9" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019de045-96cb-7b17-953e-1b54d7a8a0f2" xlink:type="arc" order="42"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-70f8-953a-b373bd7d5c90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-70f8-953a-b373bd7d5c90" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7d59-b08d-6880d087f0dd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-70f8-953a-b373bd7d5c90" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7d59-b08d-6880d087f0dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7d59-b08d-6880d087f0dd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7d59-b08d-6880d087f0dd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7d59-b08d-6880d087f0dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-712e-aeb2-e2061416283b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7d59-b08d-6880d087f0dd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-712e-aeb2-e2061416283b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-7ae2-9bf5-645a02411a26" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-712e-aeb2-e2061416283b" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-7ae2-9bf5-645a02411a26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-3a58-7488-a41c-0df28363a6d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-70f8-953a-b373bd7d5c90" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-3a58-7488-a41c-0df28363a6d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3a58-7488-a41c-0df28363a6d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3a58-7488-a41c-0df28363a6d9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3a58-7488-a41c-0df28363a6d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3a58-7dc1-b682-7a5c7d26f4a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3a58-7488-a41c-0df28363a6d9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3a58-7dc1-b682-7a5c7d26f4a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A413SeniorNotesDue2025Member_019dd587-3a58-7300-9c47-c977dc10eab3" xlink:href="dpl-20260331.xsd#dpl_A413SeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3a58-7dc1-b682-7a5c7d26f4a2" xlink:to="loc_dpl_A413SeniorNotesDue2025Member_019dd587-3a58-7300-9c47-c977dc10eab3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-7da0-b3bc-aca7e509d2b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-7da0-b3bc-aca7e509d2b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3a58-7824-82ac-2e7a36d8b19b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-7da0-b3bc-aca7e509d2b7" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3a58-7824-82ac-2e7a36d8b19b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-7da0-b3bc-aca7e509d2b7" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_019dd587-3a58-743b-b40c-268c46679b36" xlink:href="dpl-20260331.xsd#dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_019dd587-3a58-743b-b40c-268c46679b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dd587-3a58-764b-b78e-a53fe9f4c0f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dd587-3a58-764b-b78e-a53fe9f4c0f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dd587-3a58-76f6-adaf-fd3c62c4ff0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dd587-3a58-76f6-adaf-fd3c62c4ff0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation_019dd587-3a58-7adf-b4a1-d59c025babdb" xlink:href="dpl-20260331.xsd#dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation_019dd587-3a58-7adf-b4a1-d59c025babdb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_019dd587-3a58-702e-bbf8-57bfa384c425" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_019dd587-3a58-702e-bbf8-57bfa384c425" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_019dd587-3a58-7a22-80a5-4970460f9d16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_019dd587-3a58-7a22-80a5-4970460f9d16" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-70ac-a04a-bc72c8516e36" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInReceivables_019dd587-3a58-7c60-b41c-c58296f209df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInReceivables_019dd587-3a58-7c60-b41c-c58296f209df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_019dd587-3a58-7519-a9f5-1ed57d167fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_019dd587-3a58-7519-a9f5-1ed57d167fe2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_019dd587-3a58-7cd2-ba98-72f89716d6b6" xlink:href="dpl-20260331.xsd#dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_019dd587-3a58-7cd2-ba98-72f89716d6b6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_019dd587-3a58-7423-95e8-b4288039c1eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_019dd587-3a58-7423-95e8-b4288039c1eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_019dd587-3a58-78ea-9eea-05db2e9841fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_019dd587-3a58-78ea-9eea-05db2e9841fb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_019dd587-3a58-76b3-b4bf-cbd20685f3d4" xlink:href="dpl-20260331.xsd#dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_019dd587-3a58-76b3-b4bf-cbd20685f3d4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019dd587-3a58-71b3-b8e2-3c2bd1f54446" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019dd587-3a58-71b3-b8e2-3c2bd1f54446" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dd587-3a58-7622-b157-2cf814397c48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dd587-3a58-7622-b157-2cf814397c48" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019dd587-3a58-7b1e-af1a-5984cad2a30a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019dd587-3a58-7b1e-af1a-5984cad2a30a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dd587-3a58-77ce-bdc8-0803682ae232" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dd587-3a58-77ce-bdc8-0803682ae232" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019dd587-3a58-73ad-931d-de243cedeab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019dd587-3a58-73ad-931d-de243cedeab6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_019dd587-3a58-752d-8778-7dbbceebca20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_019dd587-3a58-752d-8778-7dbbceebca20" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_019dd587-3a58-787f-924a-02ee8ed45672" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-3a58-7ce8-bbf4-a02b732dde05" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_019dd587-3a58-787f-924a-02ee8ed45672" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dd587-3a58-70a3-a14a-67191a88a632" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-3a58-7da0-b3bc-aca7e509d2b7" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dd587-3a58-70a3-a14a-67191a88a632" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_019dd587-3a58-7007-94c8-2331a01be297" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_019dd587-3a58-7007-94c8-2331a01be297" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_019ddad4-057d-7350-b927-a6328f21fab8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionInAidOfConstruction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_019ddad4-057d-7350-b927-a6328f21fab8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3a58-739c-ab79-555934072ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3a58-739c-ab79-555934072ff9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates_019dd587-3a58-7987-80d8-00b5ace31221" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates_019dd587-3a58-7987-80d8-00b5ace31221" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dd587-3a58-75a6-95ff-e77ba4ebbf9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dd587-3a58-75a6-95ff-e77ba4ebbf9a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dd587-3a58-773d-b33f-19fc10d6272b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-3a58-71c9-97c0-df578e058b39" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dd587-3a58-773d-b33f-19fc10d6272b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019dd587-3a58-7f3c-9f20-dc1fc093cc1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_PaymentsOfDividends_019dd587-3a58-7f3c-9f20-dc1fc093cc1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PaymentsOfDeferredFinanceCosts_019dd587-3a58-71cc-b06f-1ac391720f61" xlink:href="dpl-20260331.xsd#dpl_PaymentsOfDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_dpl_PaymentsOfDeferredFinanceCosts_019dd587-3a58-71cc-b06f-1ac391720f61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dd587-3a58-7749-9230-541322754a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dd587-3a58-7749-9230-541322754a5b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019dd587-3a58-72c0-b358-9cf4abc79511" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019dd587-3a58-72c0-b358-9cf4abc79511" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019dd587-3a58-7d13-b61d-fc24395d9f79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019dd587-3a58-7d13-b61d-fc24395d9f79" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromShortTermDebt_019dd587-3a58-7c6b-a99a-d3d451404024" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_ProceedsFromShortTermDebt_019dd587-3a58-7c6b-a99a-d3d451404024" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfShortTermDebt_019dd587-3a58-745f-8dd5-76cd75ca84c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_RepaymentsOfShortTermDebt_019dd587-3a58-745f-8dd5-76cd75ca84c5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3a58-7a1e-930e-cecede897439" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3a58-7a1e-930e-cecede897439" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_019dd587-3a58-7ca1-81c3-42987ba5cd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_019dd587-3a58-7ca1-81c3-42987ba5cd1f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dd587-3a58-7244-933e-78fdf030585c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-3a58-7954-84fa-d7cf2fa8a0da" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dd587-3a58-7244-933e-78fdf030585c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-3a58-7863-a1be-dfc60fa3c037" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-3a58-7863-a1be-dfc60fa3c037" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dd587-3a58-75a1-b8aa-f5d7a1c98e2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-3a58-7863-a1be-dfc60fa3c037" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dd587-3a58-75a1-b8aa-f5d7a1c98e2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-3a58-7348-bee7-34c97b8e9d5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-3a58-7863-a1be-dfc60fa3c037" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-3a58-7348-bee7-34c97b8e9d5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-3a58-7d7c-9173-051353d145cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-3a58-7d7c-9173-051353d145cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019dd587-3a58-75a8-a464-c9e8d4e56e66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-3a58-7d7c-9173-051353d145cc" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019dd587-3a58-75a8-a464-c9e8d4e56e66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-3a58-7aff-8ad0-4af9c0467fda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-3a58-7aff-8ad0-4af9c0467fda" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_019dd587-3a58-7812-89e7-bc26b8374261" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-3a58-7aff-8ad0-4af9c0467fda" xlink:to="loc_us-gaap_InterestPaidNet_019dd587-3a58-7812-89e7-bc26b8374261" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019dd587-3a58-709e-b714-50f2dd54d3d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-3a58-7aff-8ad0-4af9c0467fda" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019dd587-3a58-709e-b714-50f2dd54d3d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3a58-7359-ae0f-7596d2a40496" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3a58-7359-ae0f-7596d2a40496" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019dd587-3a58-7385-b745-16e8d0fa056c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019dd587-3a58-7385-b745-16e8d0fa056c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInSecurityDeposits_019dd587-3a58-7ceb-b33f-57cead636d0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInSecurityDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_IncreaseDecreaseInSecurityDeposits_019dd587-3a58-7ceb-b33f-57cead636d0b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromInsuranceSettlementInvestingActivities_019dd587-3a58-7c9e-b448-6007472a10f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromInsuranceSettlementInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_ProceedsFromInsuranceSettlementInvestingActivities_019dd587-3a58-7c9e-b448-6007472a10f5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dd587-3a58-72a2-ac33-0ec98a21714a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dd587-3a58-72a2-ac33-0ec98a21714a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NonCashProceedsFromSaleOfBusiness_019dd587-3a58-70a2-bf33-92bdb7ed461e" xlink:href="dpl-20260331.xsd#dpl_NonCashProceedsFromSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_dpl_NonCashProceedsFromSaleOfBusiness_019dd587-3a58-70a2-bf33-92bdb7ed461e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3a58-737d-823f-a53ff5f0629f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3a58-737d-823f-a53ff5f0629f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_019dd587-3a58-7ed5-9773-63a975dd33c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_019dd587-3a58-7ed5-9773-63a975dd33c7" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dd587-3a58-7170-8cca-0e63c4d53d4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dd587-3a58-7170-8cca-0e63c4d53d4a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfOrdinaryDividends_019ddad5-d702-7d42-ba35-8440a71599e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfOrdinaryDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-768e-82d9-f06908536d16" xlink:to="loc_us-gaap_PaymentsOfOrdinaryDividends_019ddad5-d702-7d42-ba35-8440a71599e9" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/StatementofShareholdersEquityStatement" xlink:type="simple" xlink:href="dpl-20260331.xsd#StatementofShareholdersEquityStatement"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/StatementofShareholdersEquityStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7233-917f-95229393d115" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7233-917f-95229393d115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7233-917f-95229393d115_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7233-917f-95229393d115" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7233-917f-95229393d115_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-7233-917f-95229393d115" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dd587-3a58-7e7d-8c7c-47e64606b34b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_CommonStockMember_019dd587-3a58-7e7d-8c7c-47e64606b34b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3a58-7cb1-88ca-fcd8e0c06a48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAdditionalCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3a58-7cb1-88ca-fcd8e0c06a48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-7156-b94d-fcd825b9ddf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-7156-b94d-fcd825b9ddf3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019dd587-3a58-7d5d-b3a8-f14f8db1f496" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_RetainedEarningsMember_019dd587-3a58-7d5d-b3a8-f14f8db1f496" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociAttributableToNoncontrollingInterestMember_019ddae0-e3f3-701c-b9ab-57615336d680" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_AociAttributableToNoncontrollingInterestMember_019ddae0-e3f3-701c-b9ab-57615336d680" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019ddae1-c2b2-7657-881a-d7a21013dc32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7b03-b2e4-dd67ac79a2de" xlink:to="loc_us-gaap_DividendsDomain_019ddae1-c2b2-7657-881a-d7a21013dc32" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7c92-88af-4476bf4b13bd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7c92-88af-4476bf4b13bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7c92-88af-4476bf4b13bd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7c92-88af-4476bf4b13bd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7c92-88af-4476bf4b13bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-72dc-a06f-e7c905c74715" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-7c92-88af-4476bf4b13bd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-72dc-a06f-e7c905c74715" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-735e-b69f-3ab9577bae5c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-72dc-a06f-e7c905c74715" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-735e-b69f-3ab9577bae5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3a58-743d-a945-f9a511850e38" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3a58-743d-a945-f9a511850e38" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3a58-743d-a945-f9a511850e38_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3a58-743d-a945-f9a511850e38" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3a58-743d-a945-f9a511850e38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3a58-7173-afbc-83b0fa1ba2fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3a58-743d-a945-f9a511850e38" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3a58-7173-afbc-83b0fa1ba2fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-3a58-7ec1-a44e-d5e073712b62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3a58-7173-afbc-83b0fa1ba2fe" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-3a58-7ec1-a44e-d5e073712b62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3a58-7861-8d1d-b556faf8b19c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3a58-7861-8d1d-b556faf8b19c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3a58-7861-8d1d-b556faf8b19c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3a58-7861-8d1d-b556faf8b19c" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3a58-7861-8d1d-b556faf8b19c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3a58-754e-9de4-4a8e4f0865c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3a58-7861-8d1d-b556faf8b19c" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3a58-754e-9de4-4a8e4f0865c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3a58-74d0-8fe8-acc5d4a204b2" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3a58-754e-9de4-4a8e4f0865c9" xlink:to="loc_dpl_UtilityMember_019dd587-3a58-74d0-8fe8-acc5d4a204b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-70da-87b2-5d2a17b71d2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-70da-87b2-5d2a17b71d2a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-70da-87b2-5d2a17b71d2a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-70da-87b2-5d2a17b71d2a" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-70da-87b2-5d2a17b71d2a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7cae-b92e-d58cdd9f662e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-70da-87b2-5d2a17b71d2a" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7cae-b92e-d58cdd9f662e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3a58-7687-a3a8-0dbdbc1ea658" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAdditionalCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7cae-b92e-d58cdd9f662e" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3a58-7687-a3a8-0dbdbc1ea658" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMember_019dd587-3a58-7557-8e62-edca97f6b0ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7cae-b92e-d58cdd9f662e" xlink:to="loc_us-gaap_EquityMember_019dd587-3a58-7557-8e62-edca97f6b0ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-74d4-b8c9-1096c4d9f9a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7cae-b92e-d58cdd9f662e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-74d4-b8c9-1096c4d9f9a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-782f-831c-1d0790f0fb52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-782f-831c-1d0790f0fb52" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-782f-831c-1d0790f0fb52_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-782f-831c-1d0790f0fb52" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-782f-831c-1d0790f0fb52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7f6c-8af0-39d14fdaf048" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-782f-831c-1d0790f0fb52" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7f6c-8af0-39d14fdaf048" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-778f-9882-2eb474cce683" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7f6c-8af0-39d14fdaf048" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-778f-9882-2eb474cce683" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_019dd587-3a58-7ff1-89f3-9483d568bb0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_TaxPeriodAxis_019dd587-3a58-7ff1-89f3-9483d568bb0c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019dd587-3a58-7ff1-89f3-9483d568bb0c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_019dd587-3a58-7ff1-89f3-9483d568bb0c" xlink:to="loc_us-gaap_TaxPeriodDomain_019dd587-3a58-7ff1-89f3-9483d568bb0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019dd587-3a58-7ca2-b46f-bbe61f61bd6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_019dd587-3a58-7ff1-89f3-9483d568bb0c" xlink:to="loc_us-gaap_TaxPeriodDomain_019dd587-3a58-7ca2-b46f-bbe61f61bd6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMember_019dd587-3a58-7d26-a386-c9305c6de6be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_019dd587-3a58-7ca2-b46f-bbe61f61bd6c" xlink:to="loc_us-gaap_EquityMember_019dd587-3a58-7d26-a386-c9305c6de6be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019dd587-3a58-7e1c-bcbe-20f239d8db14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019dd587-3a58-7e1c-bcbe-20f239d8db14" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019dd587-3a58-7e1c-bcbe-20f239d8db14_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019dd587-3a58-7e1c-bcbe-20f239d8db14" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019dd587-3a58-7e1c-bcbe-20f239d8db14_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019dd587-3a58-733b-8416-442cad67b346" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019dd587-3a58-7e1c-bcbe-20f239d8db14" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019dd587-3a58-733b-8416-442cad67b346" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de43a-7276-73ba-b5dc-d4f91169ca9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3a58-7702-94a6-4b97ce6cb9ad" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de43a-7276-73ba-b5dc-d4f91169ca9e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de43a-7276-73ba-b5dc-d4f91169ca9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de43a-7276-73ba-b5dc-d4f91169ca9e" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de43a-7276-73ba-b5dc-d4f91169ca9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de43a-7276-7f73-9cab-6dfc36581a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de43a-7276-73ba-b5dc-d4f91169ca9e" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de43a-7276-7f73-9cab-6dfc36581a4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLMember_019de43a-7276-7bf7-95a8-5db99bd4fb41" xlink:href="dpl-20260331.xsd#dpl_DPLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de43a-7276-7f73-9cab-6dfc36581a4e" xlink:to="loc_dpl_DPLMember_019de43a-7276-7bf7-95a8-5db99bd4fb41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019dd587-3a58-7801-99bb-f0151079eb8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_SharesIssued_019dd587-3a58-7801-99bb-f0151079eb8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-7a16-ada7-3267be02c596" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-7a16-ada7-3267be02c596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7ba7-89e3-4220f6f2c27d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7ba7-89e3-4220f6f2c27d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3a58-7f0d-aef4-a4552db4a4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3a58-7f0d-aef4-a4552db4a4f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-76e2-b094-906ba3d255de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-3a58-76e2-b094-906ba3d255de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-7feb-8137-9011ae544efd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-3a58-7feb-8137-9011ae544efd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-3a58-734b-824b-9575ac5ad59c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_CommonStockValue_019dd587-3a58-734b-824b-9575ac5ad59c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-731f-a654-71bf671a7cfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-3a58-731f-a654-71bf671a7cfd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7f7b-8640-56ddee008708" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-7f7b-8640-56ddee008708" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-7809-889c-5930fdcb3b40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-3a58-7809-889c-5930fdcb3b40" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dd587-3a58-75e9-9c9e-bff044e2a5a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_StockholdersEquityOther_019dd587-3a58-75e9-9c9e-bff044e2a5a9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7c32-a583-5eaa76450c19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-3a58-7c32-a583-5eaa76450c19" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019dd587-3a58-7921-b2e5-45f142b87e06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_PaymentsOfDividends_019dd587-3a58-7921-b2e5-45f142b87e06" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-3a58-7a08-a9dc-32fab7d70cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-3a58-7a08-a9dc-32fab7d70cde" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3a58-775b-af0d-54f0199e0ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3a58-775b-af0d-54f0199e0ea7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_019dd587-3a58-79ee-807a-d377b23d135a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_MembersEquity_019dd587-3a58-79ee-807a-d377b23d135a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3a58-7ac6-b562-d7cdb662e931" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3a58-7ac6-b562-d7cdb662e931" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociTaxAttributableToParent_019dd587-3a58-7c2d-b1f3-d5f273fd294a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_AociTaxAttributableToParent_019dd587-3a58-7c2d-b1f3-d5f273fd294a" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-7e90-9bc5-7b09b733719f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3a58-7e90-9bc5-7b09b733719f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ddadd-d1d1-7526-a7ed-c2c96539639a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ddadd-d1d1-7526-a7ed-c2c96539639a" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019dd587-3a58-776e-8eb0-4a02d6b1fe97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019dd587-3a58-776e-8eb0-4a02d6b1fe97" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityOtherChanges_019dd587-3a58-792b-ba39-d7587d21f7b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityOtherChanges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_TemporaryEquityOtherChanges_019dd587-3a58-792b-ba39-d7587d21f7b9" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3a58-7fff-985f-714da7aa9523" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3a58-7fff-985f-714da7aa9523" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfOrdinaryDividends_019ddae1-8c40-7eb0-9977-ef2b53fdc5f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfOrdinaryDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_PaymentsOfOrdinaryDividends_019ddae1-8c40-7eb0-9977-ef2b53fdc5f3" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ddae3-8a15-72b1-a0c0-dd6dc343e4c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_StockholdersEquity_019ddae3-8a15-72b1-a0c0-dd6dc343e4c6" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax_019de042-155b-74f1-be8d-e7ea1c25c64f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3a58-7e4a-9937-10d6898a5053" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax_019de042-155b-74f1-be8d-e7ea1c25c64f" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/OverviewandSummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="dpl-20260331.xsd#OverviewandSummaryofSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/OverviewandSummaryofSignificantAccountingPolicies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7d9e-9d86-6f4ac939f376" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7c90-90cf-1c05cc2537d3" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7d9e-9d86-6f4ac939f376" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7c90-90cf-1c05cc2537d3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-72ba-8c5b-6fd3e86b53c0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7c90-90cf-1c05cc2537d3" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-72ba-8c5b-6fd3e86b53c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-72ba-8c5b-6fd3e86b53c0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-72ba-8c5b-6fd3e86b53c0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-72ba-8c5b-6fd3e86b53c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-732d-a86c-ef585420be83" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-72ba-8c5b-6fd3e86b53c0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-732d-a86c-ef585420be83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-7550-8622-f51a2045a5da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-732d-a86c-ef585420be83" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-7550-8622-f51a2045a5da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantAccountingPoliciesTextBlock_019dd587-3a58-7437-8bf4-1cc0a90b7a6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SignificantAccountingPoliciesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7d9e-9d86-6f4ac939f376" xlink:to="loc_us-gaap_SignificantAccountingPoliciesTextBlock_019dd587-3a58-7437-8bf4-1cc0a90b7a6c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RegulatoryMattersNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RegulatoryMattersNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7322-9c64-ab9f39d7b601" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-78f2-982c-cb635a17dbcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7322-9c64-ab9f39d7b601" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-78f2-982c-cb635a17dbcd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7608-b9a7-2d22b37ee5fd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-78f2-982c-cb635a17dbcd" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7608-b9a7-2d22b37ee5fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7608-b9a7-2d22b37ee5fd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7608-b9a7-2d22b37ee5fd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7608-b9a7-2d22b37ee5fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-721e-a530-d1b48f557fca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7608-b9a7-2d22b37ee5fd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-721e-a530-d1b48f557fca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7f9a-bdaa-e3fb90fe0bcc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-721e-a530-d1b48f557fca" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7f9a-bdaa-e3fb90fe0bcc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-3b1f-7982-8b17-2533cc15a418" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7322-9c64-ab9f39d7b601" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-3b1f-7982-8b17-2533cc15a418" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValue" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValue"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValue" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-7f0f-b900-4be563cd05c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-7795-8804-7ba62a00867b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-7f0f-b900-4be563cd05c5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-7795-8804-7ba62a00867b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fed-ab6b-03b30f73b728" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-7795-8804-7ba62a00867b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fed-ab6b-03b30f73b728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fed-ab6b-03b30f73b728_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fed-ab6b-03b30f73b728" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fed-ab6b-03b30f73b728_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7be4-a402-da381f1f310a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fed-ab6b-03b30f73b728" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7be4-a402-da381f1f310a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7cc9-ae0e-d85e4274d05c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7be4-a402-da381f1f310a" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7cc9-ae0e-d85e4274d05c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_019dd587-3b1f-7aa1-ac5e-9ecee0677dcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-7f0f-b900-4be563cd05c5" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_019dd587-3b1f-7aa1-ac5e-9ecee0677dcc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivities" xlink:type="simple" xlink:href="dpl-20260331.xsd#DerivativeInstrumentsandHedgingActivities"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivities" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-76fe-af83-a1982a8bcfb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-79f8-b72a-5b65d3e560eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-76fe-af83-a1982a8bcfb5" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-79f8-b72a-5b65d3e560eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ffc-aa6f-445ec6703636" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-79f8-b72a-5b65d3e560eb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ffc-aa6f-445ec6703636" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ffc-aa6f-445ec6703636_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ffc-aa6f-445ec6703636" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ffc-aa6f-445ec6703636_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-708c-be34-3bb29c42b3de" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ffc-aa6f-445ec6703636" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-708c-be34-3bb29c42b3de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7852-a617-1609555ad200" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-708c-be34-3bb29c42b3de" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7852-a617-1609555ad200" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_019dd587-3b1f-7124-8a7f-a502d294320c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-76fe-af83-a1982a8bcfb5" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_019dd587-3b1f-7124-8a7f-a502d294320c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtObligations" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtObligations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtObligations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-77e9-a862-9c9422be017c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-712f-adb3-1f6589f97c39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-77e9-a862-9c9422be017c" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-712f-adb3-1f6589f97c39" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7eb8-bc37-28d24aac335a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-712f-adb3-1f6589f97c39" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7eb8-bc37-28d24aac335a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7eb8-bc37-28d24aac335a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7eb8-bc37-28d24aac335a" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7eb8-bc37-28d24aac335a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-715a-9bde-9134e2712331" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7eb8-bc37-28d24aac335a" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-715a-9bde-9134e2712331" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-763e-995b-c291331828bc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-715a-9bde-9134e2712331" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-763e-995b-c291331828bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_019dd587-3b1f-7cfb-87d7-56e216455f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-77e9-a862-9c9422be017c" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_019dd587-3b1f-7cfb-87d7-56e216455f8c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxes" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-7020-9adf-5a0435c01b47" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-700a-907f-ed7adfc2fa39" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7020-9adf-5a0435c01b47" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-700a-907f-ed7adfc2fa39" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72f1-8e58-9ba917a6ce65" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-700a-907f-ed7adfc2fa39" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72f1-8e58-9ba917a6ce65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72f1-8e58-9ba917a6ce65_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72f1-8e58-9ba917a6ce65" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72f1-8e58-9ba917a6ce65_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fa0-8ca6-bab9f19160ee" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72f1-8e58-9ba917a6ce65" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fa0-8ca6-bab9f19160ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7e6b-9c3b-bf0cd154791e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fa0-8ca6-bab9f19160ee" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7e6b-9c3b-bf0cd154791e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock_019dd587-3b1f-7743-98f9-40090de7af54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7020-9adf-5a0435c01b47" xlink:to="loc_us-gaap_IncomeTaxDisclosureTextBlock_019dd587-3b1f-7743-98f9-40090de7af54" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlans" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlans"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlans" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-74a9-8fe2-953c4c1fc916" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-76b2-b2d1-a5aeaf85f096" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-74a9-8fe2-953c4c1fc916" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-76b2-b2d1-a5aeaf85f096" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7759-9b25-3395cb5e9302" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-76b2-b2d1-a5aeaf85f096" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7759-9b25-3395cb5e9302" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7759-9b25-3395cb5e9302_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7759-9b25-3395cb5e9302" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7759-9b25-3395cb5e9302_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d92-943b-92d7571a626f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7759-9b25-3395cb5e9302" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d92-943b-92d7571a626f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7ab8-a2a6-d60c290d456c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d92-943b-92d7571a626f" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7ab8-a2a6-d60c290d456c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7bf7-a35a-03931afa466f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-76b2-b2d1-a5aeaf85f096" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7bf7-a35a-03931afa466f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7bf7-a35a-03931afa466f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7bf7-a35a-03931afa466f" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7bf7-a35a-03931afa466f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7236-bfdf-cdbfba9c92fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7bf7-a35a-03931afa466f" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7236-bfdf-cdbfba9c92fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-7434-9e7c-77fd87fdc049" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7236-bfdf-cdbfba9c92fc" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-7434-9e7c-77fd87fdc049" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_019dd587-3b1f-7ad0-9574-ac2a37288b03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-74a9-8fe2-953c4c1fc916" xlink:to="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_019dd587-3b1f-7ad0-9574-ac2a37288b03" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingencies" xlink:type="simple" xlink:href="dpl-20260331.xsd#ContractualObligationsCommercialCommitmentsandContingencies"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingencies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-75f7-a562-fab8f2e553dd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-7dea-ac05-0351f1047b43" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-75f7-a562-fab8f2e553dd" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-7dea-ac05-0351f1047b43" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7416-a391-c1dc3c172c98" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-7dea-ac05-0351f1047b43" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7416-a391-c1dc3c172c98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7416-a391-c1dc3c172c98_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7416-a391-c1dc3c172c98" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7416-a391-c1dc3c172c98_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-757d-b4c0-8d38753269e0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7416-a391-c1dc3c172c98" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-757d-b4c0-8d38753269e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7c10-9a8b-d95c0e35af8d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-757d-b4c0-8d38753269e0" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7c10-9a8b-d95c0e35af8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_019dd587-3b1f-7fad-beff-267d4c0e467f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-75f7-a562-fab8f2e553dd" xlink:to="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_019dd587-3b1f-7fad-beff-267d4c0e467f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegments" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegments"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegments" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7f97-9346-3e00ac4be92d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7f97-9346-3e00ac4be92d" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c53-91c0-696c4e87acaa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c53-91c0-696c4e87acaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7c53-91c0-696c4e87acaa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c53-91c0-696c4e87acaa" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7c53-91c0-696c4e87acaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7699-b7cc-406d600a96fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c53-91c0-696c4e87acaa" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7699-b7cc-406d600a96fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7fd2-afe3-44eb529b13a1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7699-b7cc-406d600a96fe" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7fd2-afe3-44eb529b13a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7166-b2e3-14695b9047c5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7166-b2e3-14695b9047c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7166-b2e3-14695b9047c5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7166-b2e3-14695b9047c5" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7166-b2e3-14695b9047c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7fee-ba06-75d1cb8c6ecf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7166-b2e3-14695b9047c5" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7fee-ba06-75d1cb8c6ecf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7f98-9c04-56f0c70169ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:to="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7f98-9c04-56f0c70169ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7f98-9c04-56f0c70169ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7f98-9c04-56f0c70169ec" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7f98-9c04-56f0c70169ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7249-a69e-93625b25c172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7f98-9c04-56f0c70169ec" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7249-a69e-93625b25c172" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-718d-8fa1-ba106aa1ca35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-76ae-ae2e-6a78bccb70a1" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-718d-8fa1-ba106aa1ca35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-718d-8fa1-ba106aa1ca35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-718d-8fa1-ba106aa1ca35" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-718d-8fa1-ba106aa1ca35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-70cf-a635-0640ca12646a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-718d-8fa1-ba106aa1ca35" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-70cf-a635-0640ca12646a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_019dd587-3b1f-7556-a09b-70ace51ebb18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7f97-9346-3e00ac4be92d" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_019dd587-3b1f-7556-a09b-70ace51ebb18" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a82-a23a-b3fdbdadaa49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-76d5-98f6-82fccb661a43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a82-a23a-b3fdbdadaa49" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-76d5-98f6-82fccb661a43" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74a9-a4b9-941a7be38f09" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-76d5-98f6-82fccb661a43" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74a9-a4b9-941a7be38f09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-74a9-a4b9-941a7be38f09_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74a9-a4b9-941a7be38f09" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-74a9-a4b9-941a7be38f09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77e3-9f8a-7b4beb45b901" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74a9-a4b9-941a7be38f09" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77e3-9f8a-7b4beb45b901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7003-ade2-3e50304c7ac8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77e3-9f8a-7b4beb45b901" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7003-ade2-3e50304c7ac8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_019dd587-3b1f-7269-b022-d0a72e64de10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a82-a23a-b3fdbdadaa49" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_019dd587-3b1f-7269-b022-d0a72e64de10" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FixedassetImpairmentNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#FixedassetImpairmentNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FixedassetImpairmentNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dd587-3b1f-74bd-abb2-f4a11dc71bdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-3b1f-7c25-a4fa-a61ca06aca0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dd587-3b1f-74bd-abb2-f4a11dc71bdf" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-3b1f-7c25-a4fa-a61ca06aca0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fdb-aa08-a06c2062c577" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-3b1f-7c25-a4fa-a61ca06aca0d" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fdb-aa08-a06c2062c577" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fdb-aa08-a06c2062c577_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fdb-aa08-a06c2062c577" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fdb-aa08-a06c2062c577_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7f6f-9cb3-9ebfe0d514a2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fdb-aa08-a06c2062c577" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7f6f-9cb3-9ebfe0d514a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7996-b4e1-cf1052133335" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7f6f-9cb3-9ebfe0d514a2" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7996-b4e1-cf1052133335" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperations" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-78ad-b420-4fecdcdb6399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-78ad-b420-4fecdcdb6399" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7416-ac9e-c21904b9053e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7416-ac9e-c21904b9053e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7f3b-b6a6-0e785e215316" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7f3b-b6a6-0e785e215316" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7786-b26f-71385036f5b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7786-b26f-71385036f5b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7ecc-8295-2e4e9f69e83d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7ecc-8295-2e4e9f69e83d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-76af-a011-22b53dc48adb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-76af-a011-22b53dc48adb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperations_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperations_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperations_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-78ad-b420-4fecdcdb6399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-78ad-b420-4fecdcdb6399" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7416-ac9e-c21904b9053e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7416-ac9e-c21904b9053e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7f3b-b6a6-0e785e215316" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7416-ac9e-c21904b9053e" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7f3b-b6a6-0e785e215316" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7fc9-9dba-5c7966a2e718" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7786-b26f-71385036f5b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7786-b26f-71385036f5b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7ecc-8295-2e4e9f69e83d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7786-b26f-71385036f5b6" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7ecc-8295-2e4e9f69e83d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RiskUncertaintiesNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RiskUncertaintiesNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RiskUncertaintiesNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-3b1f-7d53-b632-f61ce21fa8d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-795c-996c-cec77a5dd3ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-3b1f-7d53-b632-f61ce21fa8d0" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-795c-996c-cec77a5dd3ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7448-9259-faa7918cd075" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-795c-996c-cec77a5dd3ed" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7448-9259-faa7918cd075" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7448-9259-faa7918cd075_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7448-9259-faa7918cd075" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7448-9259-faa7918cd075_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7685-add3-f8184d80bab0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7448-9259-faa7918cd075" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7685-add3-f8184d80bab0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7639-bfd2-75f3dde23d4c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7685-add3-f8184d80bab0" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7639-bfd2-75f3dde23d4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-3b1f-754d-a67f-ce030ff3741c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-795c-996c-cec77a5dd3ed" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-3b1f-754d-a67f-ce030ff3741c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-3b1f-754d-a67f-ce030ff3741c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-3b1f-754d-a67f-ce030ff3741c" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-3b1f-754d-a67f-ce030ff3741c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-3b1f-7263-9c89-f0dfb6d61c5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-3b1f-754d-a67f-ce030ff3741c" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-3b1f-7263-9c89-f0dfb6d61c5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RisksandUncertaintiesTextBlock_019dd587-3b1f-7aea-b5f3-0e604203ae8d" xlink:href="dpl-20260331.xsd#dpl_RisksandUncertaintiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-3b1f-7d53-b632-f61ce21fa8d0" xlink:to="loc_dpl_RisksandUncertaintiesTextBlock_019dd587-3b1f-7aea-b5f3-0e604203ae8d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesPolicy" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesPolicy"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesPolicy" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7888-b952-cb499f92d472" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7888-b952-cb499f92d472" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-79bd-b7fa-211323692347" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7888-b952-cb499f92d472" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-79bd-b7fa-211323692347" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-79bd-b7fa-211323692347_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-79bd-b7fa-211323692347" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-79bd-b7fa-211323692347_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-78bc-b817-5b9bdc373dcf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-79bd-b7fa-211323692347" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-78bc-b817-5b9bdc373dcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-709a-a260-b837e94e391a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-78bc-b817-5b9bdc373dcf" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-709a-a260-b837e94e391a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryPolicyTextBlock_019dd587-3a58-7898-9e77-13d537a23e4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_us-gaap_InventoryPolicyTextBlock_019dd587-3a58-7898-9e77-13d537a23e4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NatureOfOperations_019dd587-3a58-70fd-96f0-b9a919be24bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NatureOfOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_us-gaap_NatureOfOperations_019dd587-3a58-70fd-96f0-b9a919be24bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_019dd587-3a58-7c40-88ed-bc79df099345" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_019dd587-3a58-7c40-88ed-bc79df099345" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryIncomeTaxesPolicy_019dd587-3a58-7324-95c5-9adc602c7be8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryIncomeTaxesPolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_us-gaap_RegulatoryIncomeTaxesPolicy_019dd587-3a58-7324-95c5-9adc602c7be8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-3a58-7e18-9b56-ca55f5cb0a9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7bb2-8c74-5b36268d21fe" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-3a58-7e18-9b56-ca55f5cb0a9c" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dd587-3a58-7232-84e1-7060ce3ffd6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dd587-3a58-7232-84e1-7060ce3ffd6a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-752f-80bb-4b294a085729" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dd587-3a58-7232-84e1-7060ce3ffd6a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-752f-80bb-4b294a085729" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-752f-80bb-4b294a085729_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-752f-80bb-4b294a085729" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-752f-80bb-4b294a085729_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7ec6-be65-48b54fd2bc9c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-752f-80bb-4b294a085729" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7ec6-be65-48b54fd2bc9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-720f-ad94-8d5e277bcb8b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-7ec6-be65-48b54fd2bc9c" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-720f-ad94-8d5e277bcb8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_019dd587-3a58-70f3-bca3-8d9fff0a0fec" xlink:href="dpl-20260331.xsd#dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_019dd587-3a58-70f3-bca3-8d9fff0a0fec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_019dd587-3a58-7ce1-a84c-3f0d0cc899db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_019dd587-3a58-7ce1-a84c-3f0d0cc899db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_019dd587-3a58-71cf-a959-3e7da8777d18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_019dd587-3a58-71cf-a959-3e7da8777d18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_019dd587-3a58-76c5-9633-560cac2ebb1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_019dd587-3a58-76c5-9633-560cac2ebb1c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_019dd587-3a58-7532-943d-6f22b96932a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_019dd587-3a58-7532-943d-6f22b96932a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-3a58-7d7f-b5ff-254cd38476d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-3a58-7d7f-b5ff-254cd38476d8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_019dd587-3a58-713d-a750-b6cef46495a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_019dd587-3a58-713d-a750-b6cef46495a2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_019dd587-3a58-7695-aa81-1cf5f15975de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-3a58-77a7-8672-dd5d68307baf" xlink:to="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_019dd587-3a58-7695-aa81-1cf5f15975de" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-78a0-b72a-a526cc1bb0fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-78a0-b72a-a526cc1bb0fe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7876-8031-f1d859e62363" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-3b1f-78a0-b72a-a526cc1bb0fe" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7876-8031-f1d859e62363" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7876-8031-f1d859e62363_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7876-8031-f1d859e62363" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7876-8031-f1d859e62363_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-799f-91fe-a162381293af" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7876-8031-f1d859e62363" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-799f-91fe-a162381293af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7965-b5f6-53db79169373" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-799f-91fe-a162381293af" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7965-b5f6-53db79169373" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_019dd587-3b1f-71b8-8033-d454b92d7ab4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_019dd587-3b1f-71b8-8033-d454b92d7ab4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_019dd587-3b1f-745f-8b68-88f69e7da8fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_019dd587-3b1f-745f-8b68-88f69e7da8fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock_019dd587-3b1f-72eb-9663-cedc258473a5" xlink:href="dpl-20260331.xsd#dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:to="loc_dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock_019dd587-3b1f-72eb-9663-cedc258473a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_019dd587-3b1f-7f9e-b5e3-6472cae40458" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-3b1f-755b-ad54-2ad089de2fac" xlink:to="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_019dd587-3b1f-7f9e-b5e3-6472cae40458" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#DerivativeInstrumentsandHedgingActivitiesTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-7c56-9723-934de64eb4ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-71eb-8e3a-d99661feb2e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-7c56-9723-934de64eb4ff" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-71eb-8e3a-d99661feb2e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-777f-bc66-4c5dd3ac61f6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019dd587-3b1f-71eb-8e3a-d99661feb2e9" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-777f-bc66-4c5dd3ac61f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-777f-bc66-4c5dd3ac61f6_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-777f-bc66-4c5dd3ac61f6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-777f-bc66-4c5dd3ac61f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7496-b5bb-2b84a53fd39b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-777f-bc66-4c5dd3ac61f6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7496-b5bb-2b84a53fd39b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7f8e-9701-421e90875584" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7496-b5bb-2b84a53fd39b" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7f8e-9701-421e90875584" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock_019dd587-3b1f-70f0-a921-dde1deb0df67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019dd587-3b1f-7c56-9723-934de64eb4ff" xlink:to="loc_us-gaap_ScheduleOfDerivativeInstrumentsEffectOnOtherComprehensiveIncomeLossTableTextBlock_019dd587-3b1f-70f0-a921-dde1deb0df67" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7386-af88-b2d632b795fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-74d8-95fc-5bd5534c9b27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7386-af88-b2d632b795fa" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-74d8-95fc-5bd5534c9b27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-74d8-95fc-5bd5534c9b27" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d0f-9d54-afdef0f96937" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7a6a-a76a-2d6770aa7e2c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d0f-9d54-afdef0f96937" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-71f2-af14-6c9fdd812b32" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7d0f-9d54-afdef0f96937" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-71f2-af14-6c9fdd812b32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_019dd587-3b1f-7eda-a749-3ab52ef23df4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7386-af88-b2d632b795fa" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_019dd587-3b1f-7eda-a749-3ab52ef23df4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_019dd587-3b1f-7df8-a4c9-eb0981345f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDebtInstrumentsTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7386-af88-b2d632b795fa" xlink:to="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_019dd587-3b1f-7df8-a4c9-eb0981345f8c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxesTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-7943-8c5e-3675359f02ee" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-7801-9281-a771e61ff2dc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7943-8c5e-3675359f02ee" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-7801-9281-a771e61ff2dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7171-9324-48c095cc7dac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-7801-9281-a771e61ff2dc" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7171-9324-48c095cc7dac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7171-9324-48c095cc7dac_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7171-9324-48c095cc7dac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7171-9324-48c095cc7dac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76dc-b0df-a811d5f5670e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7171-9324-48c095cc7dac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76dc-b0df-a811d5f5670e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-784a-893d-b09f129fc08d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76dc-b0df-a811d5f5670e" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-784a-893d-b09f129fc08d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-7573-98ef-62312cc0c92d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-74fc-ae11-ec6b5a010c95" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7573-98ef-62312cc0c92d" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-74fc-ae11-ec6b5a010c95" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70fa-a40c-db5cb64c6b81" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-74fc-ae11-ec6b5a010c95" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70fa-a40c-db5cb64c6b81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70fa-a40c-db5cb64c6b81_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70fa-a40c-db5cb64c6b81" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70fa-a40c-db5cb64c6b81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76a9-b179-f1683e1182a6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70fa-a40c-db5cb64c6b81" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76a9-b179-f1683e1182a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-79e3-b63c-77b91a9ca5aa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-76a9-b179-f1683e1182a6" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-79e3-b63c-77b91a9ca5aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_019dd587-3b1f-7af3-a31f-1f2ba8c35898" xlink:href="dpl-20260331.xsd#dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7573-98ef-62312cc0c92d" xlink:to="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_019dd587-3b1f-7af3-a31f-1f2ba8c35898" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-72ee-9b3c-e2c51b160e44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-72ee-9b3c-e2c51b160e44" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75e1-a546-5c45be09c251" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75e1-a546-5c45be09c251" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-75e1-a546-5c45be09c251_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75e1-a546-5c45be09c251" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-75e1-a546-5c45be09c251_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a25-bf43-c464c88cb73d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75e1-a546-5c45be09c251" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a25-bf43-c464c88cb73d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7cf8-975c-fe03e1112417" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a25-bf43-c464c88cb73d" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7cf8-975c-fe03e1112417" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7bd5-b4f2-86f4fbaab720" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7bd5-b4f2-86f4fbaab720" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7bd5-b4f2-86f4fbaab720_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7bd5-b4f2-86f4fbaab720" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7bd5-b4f2-86f4fbaab720_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7bfd-951c-bb1ce68fbe82" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7bd5-b4f2-86f4fbaab720" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7bfd-951c-bb1ce68fbe82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7867-aca6-9f5f133fc1de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:to="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7867-aca6-9f5f133fc1de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7867-aca6-9f5f133fc1de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7867-aca6-9f5f133fc1de" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7867-aca6-9f5f133fc1de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7008-8594-e661007c2b2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-3b1f-7867-aca6-9f5f133fc1de" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-3b1f-7008-8594-e661007c2b2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-7269-b47d-669f698a2109" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7e87-be38-5fc2ba3b00e5" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-7269-b47d-669f698a2109" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-7269-b47d-669f698a2109_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-7269-b47d-669f698a2109" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-7269-b47d-669f698a2109_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-70b5-85ec-8aaeb93e1cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-3b1f-7269-b47d-669f698a2109" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-3b1f-70b5-85ec-8aaeb93e1cb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_019dd587-3b1f-7dad-bbab-f3377fb4bc72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-72ee-9b3c-e2c51b160e44" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_019dd587-3b1f-7dad-bbab-f3377fb4bc72" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a26-87b4-1bb7523560e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-7900-9de6-6099535a5ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a26-87b4-1bb7523560e5" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-7900-9de6-6099535a5ee2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecd-b76f-4b3d01cd632b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7900-9de6-6099535a5ee2" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecd-b76f-4b3d01cd632b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ecd-b76f-4b3d01cd632b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecd-b76f-4b3d01cd632b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ecd-b76f-4b3d01cd632b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-ab62-2f9d5b346896" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecd-b76f-4b3d01cd632b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-ab62-2f9d5b346896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-70ed-806b-b144a141d581" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-ab62-2f9d5b346896" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-70ed-806b-b144a141d581" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_019dd587-3b1f-7edc-9718-d35d71a15821" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a26-87b4-1bb7523560e5" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_019dd587-3b1f-7edc-9718-d35d71a15821" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7fda-b098-085e7f6d23f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7fda-b098-085e7f6d23f8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7dd9-83b2-2e04f8195bbf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7dd9-83b2-2e04f8195bbf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-78e0-b8b6-52e0b6fe871c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-78e0-b8b6-52e0b6fe871c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-773c-b21b-152f55f93429" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-773c-b21b-152f55f93429" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-73c5-9027-0a32cc16d54e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-73c5-9027-0a32cc16d54e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsTables_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsTables_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsTables_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7fda-b098-085e7f6d23f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7fda-b098-085e7f6d23f8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7dd9-83b2-2e04f8195bbf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7dd9-83b2-2e04f8195bbf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-78e0-b8b6-52e0b6fe871c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7dd9-83b2-2e04f8195bbf" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-78e0-b8b6-52e0b6fe871c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-7283-9dab-dee8f9a93eaf" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-773c-b21b-152f55f93429" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7f8d-b1fa-3a9986d9dd05" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-773c-b21b-152f55f93429" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dd587-3a58-7786-9d13-ad8f4fb8d26a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_CreditFacilityAxis_019dd587-3a58-7786-9d13-ad8f4fb8d26a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd587-3a58-7786-9d13-ad8f4fb8d26a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd587-3a58-7786-9d13-ad8f4fb8d26a" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd587-3a58-7786-9d13-ad8f4fb8d26a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd587-3a58-71d7-b50b-3742a8cfe5fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd587-3a58-7786-9d13-ad8f4fb8d26a" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd587-3a58-71d7-b50b-3742a8cfe5fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-715f-ac31-a822afaef611" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-715f-ac31-a822afaef611" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-715f-ac31-a822afaef611_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-715f-ac31-a822afaef611" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-715f-ac31-a822afaef611_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-75e7-b7af-d08bf8e55b39" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3a58-715f-ac31-a822afaef611" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-75e7-b7af-d08bf8e55b39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3a58-71d5-b183-ada80496a21b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3a58-75e7-b7af-d08bf8e55b39" xlink:to="loc_srt_SubsidiariesMember_019dd587-3a58-71d5-b183-ada80496a21b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7201-bd94-5abdc0efea84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7201-bd94-5abdc0efea84" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7201-bd94-5abdc0efea84_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7201-bd94-5abdc0efea84" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-7201-bd94-5abdc0efea84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-78e9-9776-734384438e78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-3a58-7201-bd94-5abdc0efea84" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-78e9-9776-734384438e78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-79aa-a2b3-8223c9ffe36b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-3a58-78e9-9776-734384438e78" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-79aa-a2b3-8223c9ffe36b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-70b1-9c48-11d9c2aa15bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-70b1-9c48-11d9c2aa15bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-70b1-9c48-11d9c2aa15bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-70b1-9c48-11d9c2aa15bf" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-70b1-9c48-11d9c2aa15bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7dc0-9ac1-3a823ef421be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3a58-70b1-9c48-11d9c2aa15bf" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7dc0-9ac1-3a823ef421be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3a58-7288-bdba-86ad0f82e2ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7dc0-9ac1-3a823ef421be" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3a58-7288-bdba-86ad0f82e2ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3a58-7055-b951-0119124c7ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3a58-7dc0-9ac1-3a823ef421be" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3a58-7055-b951-0119124c7ae9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-794d-847f-9171f1e36b28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-794d-847f-9171f1e36b28" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-794d-847f-9171f1e36b28_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-794d-847f-9171f1e36b28" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-794d-847f-9171f1e36b28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7195-8f7a-affd47dadee2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3a58-794d-847f-9171f1e36b28" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7195-8f7a-affd47dadee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3a58-77d7-9841-91c035328a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3a58-7195-8f7a-affd47dadee2" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-3a58-77d7-9841-91c035328a4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-3a58-7039-84e4-6dea21e28074" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-3a58-7039-84e4-6dea21e28074" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7039-84e4-6dea21e28074_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-3a58-7039-84e4-6dea21e28074" xlink:to="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7039-84e4-6dea21e28074_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7a74-8467-d3e5620b3706" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-3a58-7039-84e4-6dea21e28074" xlink:to="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7a74-8467-d3e5620b3706" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019dd587-3a58-74ad-85bb-2a4d7d1360cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7a74-8467-d3e5620b3706" xlink:to="loc_us-gaap_NonrelatedPartyMember_019dd587-3a58-74ad-85bb-2a4d7d1360cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-3a58-7a34-9247-f68c57be34ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dd587-3a58-7a74-8467-d3e5620b3706" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-3a58-7a34-9247-f68c57be34ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3a58-7242-a335-8bc6dc631553" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3a58-7242-a335-8bc6dc631553" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3a58-7242-a335-8bc6dc631553_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3a58-7242-a335-8bc6dc631553" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3a58-7242-a335-8bc6dc631553_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3a58-7b2e-941f-cf6c7e0211a8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3a58-7242-a335-8bc6dc631553" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3a58-7b2e-941f-cf6c7e0211a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3a58-7eae-bfef-61a00588deee" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3a58-7b2e-941f-cf6c7e0211a8" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3a58-7eae-bfef-61a00588deee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dd587-3a58-7ff3-ac12-f1392c8d3c78" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_dei_LegalEntityAxis_019dd587-3a58-7ff3-ac12-f1392c8d3c78" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-3a58-7ff3-ac12-f1392c8d3c78_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dd587-3a58-7ff3-ac12-f1392c8d3c78" xlink:to="loc_dei_EntityDomain_019dd587-3a58-7ff3-ac12-f1392c8d3c78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-3a58-7364-8fe2-b17c49bef1d8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dd587-3a58-7ff3-ac12-f1392c8d3c78" xlink:to="loc_dei_EntityDomain_019dd587-3a58-7364-8fe2-b17c49bef1d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQMember_019dd587-3a58-7ea0-a2e7-4c471211df5b" xlink:href="dpl-20260331.xsd#dpl_CDPQMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3a58-7364-8fe2-b17c49bef1d8" xlink:to="loc_dpl_CDPQMember_019dd587-3a58-7ea0-a2e7-4c471211df5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsMember_019dd587-3a58-7749-bce5-b1b9c87956a4" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3a58-7364-8fe2-b17c49bef1d8" xlink:to="loc_dpl_OhioHoldingsMember_019dd587-3a58-7749-bce5-b1b9c87956a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsMember_019dd587-3a58-7612-8e48-1c832c27a590" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3a58-7364-8fe2-b17c49bef1d8" xlink:to="loc_dpl_OhioInvestmentsMember_019dd587-3a58-7612-8e48-1c832c27a590" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-774a-b6fb-5c0ad99e781a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-774a-b6fb-5c0ad99e781a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-774a-b6fb-5c0ad99e781a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-774a-b6fb-5c0ad99e781a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-774a-b6fb-5c0ad99e781a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7655-bd94-e0526a3a724e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3a58-774a-b6fb-5c0ad99e781a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7655-bd94-e0526a3a724e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-796f-a7de-14e5c172e6ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3a58-7655-bd94-e0526a3a724e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-796f-a7de-14e5c172e6ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-799b-88a8-8b716a412c55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-799b-88a8-8b716a412c55" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-799b-88a8-8b716a412c55_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-799b-88a8-8b716a412c55" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-799b-88a8-8b716a412c55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7991-a795-15f6d037115e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3a58-799b-88a8-8b716a412c55" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7991-a795-15f6d037115e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-71c9-bcf7-23efaab1963e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7991-a795-15f6d037115e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3a58-71c9-bcf7-23efaab1963e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_naics_ZZ525110_019dd587-3a58-766d-b95c-2e2d8152e144" xlink:href="https://xbrl.sec.gov/naics/2026/naics-2026.xsd#naics_ZZ525110"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7991-a795-15f6d037115e" xlink:to="loc_naics_ZZ525110_019dd587-3a58-766d-b95c-2e2d8152e144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019dd587-3a58-79a6-bbd2-dbb26a700c6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3a58-7991-a795-15f6d037115e" xlink:to="loc_us-gaap_CashFlowHedgingMember_019dd587-3a58-79a6-bbd2-dbb26a700c6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019dd587-3a58-764d-a08f-17b03cd0df58" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-3a58-7d1e-b45a-dc4c46a0150a" xlink:to="loc_srt_OwnershipAxis_019dd587-3a58-764d-a08f-17b03cd0df58" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-3a58-764d-a08f-17b03cd0df58_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019dd587-3a58-764d-a08f-17b03cd0df58" xlink:to="loc_srt_OwnershipDomain_019dd587-3a58-764d-a08f-17b03cd0df58_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-3a58-7ef7-8648-92e3010bc876" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019dd587-3a58-764d-a08f-17b03cd0df58" xlink:to="loc_srt_OwnershipDomain_019dd587-3a58-7ef7-8648-92e3010bc876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsMember_019dd587-3a58-7cda-bb03-d54c819050f3" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-3a58-7ef7-8648-92e3010bc876" xlink:to="loc_dpl_OhioHoldingsMember_019dd587-3a58-7cda-bb03-d54c819050f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsMember_019dd587-3a58-774b-9287-ef1295add49e" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-3a58-7ef7-8648-92e3010bc876" xlink:to="loc_dpl_OhioInvestmentsMember_019dd587-3a58-774b-9287-ef1295add49e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLMember_019dd587-3a58-7b77-a521-a942ad2a3699" xlink:href="dpl-20260331.xsd#dpl_DPLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-3a58-7ef7-8648-92e3010bc876" xlink:to="loc_dpl_DPLMember_019dd587-3a58-7b77-a521-a942ad2a3699" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019dd587-3a58-7418-85dd-046b96e8651c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_NumberOfReportableSegments_019dd587-3a58-7418-85dd-046b96e8651c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7a49-a9db-d95eead59a59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-3a58-7a49-a9db-d95eead59a59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_019dd587-3a58-7219-a4bd-14a6742043ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_RestrictedCash_019dd587-3a58-7219-a4bd-14a6742043ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_019dd587-3a58-7718-9232-14b824d96e01" xlink:href="dpl-20260331.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_NumberOfRetailCustomers_019dd587-3a58-7718-9232-14b824d96e01" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_019dd587-3a58-7ddc-a653-4e37d3a95c24" xlink:href="dpl-20260331.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_ServiceAreaSquareMiles_019dd587-3a58-7ddc-a653-4e37d3a95c24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019dd587-3a58-7e37-99a5-6102c72461e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019dd587-3a58-7e37-99a5-6102c72461e6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExciseTaxesCollected_019dd587-3a58-7f30-98f4-29680e15fb76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExciseTaxesCollected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ExciseTaxesCollected_019dd587-3a58-7f30-98f4-29680e15fb76" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CustomerReceivables_019dd587-3a58-7215-8c2e-e610a965af07" xlink:href="dpl-20260331.xsd#dpl_CustomerReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_CustomerReceivables_019dd587-3a58-7215-8c2e-e610a965af07" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UnbilledRevenue_019dd587-3a58-7d8b-9b22-0f88796a0e66" xlink:href="dpl-20260331.xsd#dpl_UnbilledRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_UnbilledRevenue_019dd587-3a58-7d8b-9b22-0f88796a0e66" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DuefromPJMtransmissionsettlement_019dd587-3a58-7f62-84da-1e1ed3f996cf" xlink:href="dpl-20260331.xsd#dpl_DuefromPJMtransmissionsettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_DuefromPJMtransmissionsettlement_019dd587-3a58-7f62-84da-1e1ed3f996cf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivables_019dd587-3a58-73c4-9684-c4a7b05075fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherReceivables_019dd587-3a58-73c4-9684-c4a7b05075fe" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-3a58-7e5b-9a18-e228d05fb3cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-3a58-7e5b-9a18-e228d05fb3cb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNet_019ddb14-2398-7992-9c67-4c005eb390e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AccountsReceivableNet_019ddb14-2398-7992-9c67-4c005eb390e9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-75a0-998f-0ba93bef18f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-3a58-75a0-998f-0ba93bef18f5" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_019dd587-3a58-738c-b408-31397f1a32f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_019dd587-3a58-738c-b408-31397f1a32f6" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_019dd587-3a58-7380-91af-db914c16d360" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_019dd587-3a58-7380-91af-db914c16d360" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_019dd587-3a58-7a04-af1f-bfa7c80a3d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_019dd587-3a58-7a04-af1f-bfa7c80a3d3d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-3a58-7c71-9cf7-b04ff8bd1f78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-3a58-7c71-9cf7-b04ff8bd1f78" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3a58-76f4-ab03-83e59206356e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3a58-76f4-ab03-83e59206356e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3a58-7496-8dae-64fe6b5d59c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3a58-7496-8dae-64fe6b5d59c2" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dd587-3a58-724c-b9f5-7e217097d1b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dd587-3a58-724c-b9f5-7e217097d1b5" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-700c-9edd-25a549f60c4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-700c-9edd-25a549f60c4e" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-79ae-9f3b-df2cb60feff6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3a58-79ae-9f3b-df2cb60feff6" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019dd587-3a58-7130-acb2-57b9a377a79b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019dd587-3a58-7130-acb2-57b9a377a79b" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToNoncontrollingInterest_019dd587-3a58-7939-956a-a8a2012e1537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentBeforeTaxPortionAttributableToNoncontrollingInterest_019dd587-3a58-7939-956a-a8a2012e1537" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-3a58-7d85-be90-6691a1296bae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-3a58-7d85-be90-6691a1296bae" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-3a58-7f55-a3d3-059043e2875a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-3a58-7f55-a3d3-059043e2875a" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-3a58-70e3-8fc7-a0640eafd521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-3a58-70e3-8fc7-a0640eafd521" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-756e-b61e-1615d0470067" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-3a58-756e-b61e-1615d0470067" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-7740-930c-932ae043747a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3a58-7740-930c-932ae043747a" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-3a58-70eb-be13-bf2ad316c650" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-3a58-70eb-be13-bf2ad316c650" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-3a58-7b41-8161-428f4ced5790" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-3a58-7b41-8161-428f4ced5790" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_019dd587-3a58-7791-a5f6-d5d4b1e576f8" xlink:href="dpl-20260331.xsd#dpl_AllowanceForFundsUsedDuringConstructionEquityPortion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_019dd587-3a58-7791-a5f6-d5d4b1e576f8" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalizedAdjustment_019dd587-3a58-71cb-ae5f-7f7307f36e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalizedAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_InterestCostsCapitalizedAdjustment_019dd587-3a58-71cb-ae5f-7f7307f36e9c" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalized_019dd587-3a58-7714-883a-f5878e835604" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_InterestCostsCapitalized_019dd587-3a58-7714-883a-f5878e835604" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_019dd587-3a58-7dad-832e-caca3623c1b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_019dd587-3a58-7dad-832e-caca3623c1b4" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-3a58-71f6-a1ef-fc706724bc95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-3a58-71f6-a1ef-fc706724bc95" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsPurchasePrice_019dd587-3a58-77a7-94a2-02bf39477439" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_OhioHoldingsPurchasePrice_019dd587-3a58-77a7-94a2-02bf39477439" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsPurchasePrice_019dd587-3a58-783a-822a-ec3fa05ca18e" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_OhioInvestmentsPurchasePrice_019dd587-3a58-783a-822a-ec3fa05ca18e" xlink:type="arc" order="38"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentTotal_019dd587-3a58-75ed-8527-1ebdd858e2d2" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_CDPQInvestmentTotal_019dd587-3a58-75ed-8527-1ebdd858e2d2" xlink:type="arc" order="39"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsInvestmentPercent_019dd587-3a58-7d47-b941-204aa95fa489" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_OhioHoldingsInvestmentPercent_019dd587-3a58-7d47-b941-204aa95fa489" xlink:type="arc" order="40"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentPercent_019dd587-3a58-7360-8847-8f65238dc0a6" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_OhioInvestmentPercent_019dd587-3a58-7360-8847-8f65238dc0a6" xlink:type="arc" order="41"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentPercent_019dd587-3a58-705e-a69a-093ca31c46f2" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_dpl_CDPQInvestmentPercent_019dd587-3a58-705e-a69a-093ca31c46f2" xlink:type="arc" order="42"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3a58-7cb7-8bca-345f4f132cc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3a58-7cb7-8bca-345f4f132cc7" xlink:type="arc" order="43"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3a58-757d-a987-3043289ac43c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-3a58-7ffb-aa35-ed4e4df34d0c" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3a58-757d-a987-3043289ac43c" xlink:type="arc" order="44"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019dd587-3a58-76c7-907d-c147208e12ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019dd587-3a58-76c7-907d-c147208e12ef" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-7185-a11b-553bce5b3d1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-3a58-7185-a11b-553bce5b3d1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-722d-a7bf-f0a18dd0ea20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-3a58-722d-a7bf-f0a18dd0ea20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PropertyPlantAndEquipmentNetOfDepreciation_019dd587-3a58-7e32-88d8-22d59d1263fc" xlink:href="dpl-20260331.xsd#dpl_PropertyPlantAndEquipmentNetOfDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:to="loc_dpl_PropertyPlantAndEquipmentNetOfDepreciation_019dd587-3a58-7e32-88d8-22d59d1263fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019dd587-3a58-7a60-b48c-ed70e1aa0fb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-3a58-7c63-ae74-c26180ed609e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019dd587-3a58-7a60-b48c-ed70e1aa0fb2" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RegulatoryMattersDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RegulatoryMattersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-7358-9951-1e55d01572a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-7358-9951-1e55d01572a0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b5d-88db-81682174260c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7358-9951-1e55d01572a0" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b5d-88db-81682174260c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b5d-88db-81682174260c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b5d-88db-81682174260c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b5d-88db-81682174260c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b5a-9084-a88949196aea" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b5d-88db-81682174260c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b5a-9084-a88949196aea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7fec-b766-ad739284dd4a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b5a-9084-a88949196aea" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7fec-b766-ad739284dd4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetAxis_019dd587-3b1f-7aea-985a-6ef8cf759c94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7358-9951-1e55d01572a0" xlink:to="loc_us-gaap_RegulatoryAssetAxis_019dd587-3b1f-7aea-985a-6ef8cf759c94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7aea-985a-6ef8cf759c94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryAssetAxis_019dd587-3b1f-7aea-985a-6ef8cf759c94" xlink:to="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7aea-985a-6ef8cf759c94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7c98-a3f4-000c956b9ace" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryAssetAxis_019dd587-3b1f-7aea-985a-6ef8cf759c94" xlink:to="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7c98-a3f4-000c956b9ace" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UnrecoveredOVECChargesMember_019dd587-3b1f-71de-8526-ccbd561bc0c2" xlink:href="dpl-20260331.xsd#dpl_UnrecoveredOVECChargesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7c98-a3f4-000c956b9ace" xlink:to="loc_dpl_UnrecoveredOVECChargesMember_019dd587-3b1f-71de-8526-ccbd561bc0c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_COVID19DeferralMember_019dd587-3b1f-7ae0-942f-204aed3d01fe" xlink:href="dpl-20260331.xsd#dpl_COVID19DeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_019dd587-3b1f-7c98-a3f4-000c956b9ace" xlink:to="loc_dpl_COVID19DeferralMember_019dd587-3b1f-7ae0-942f-204aed3d01fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-79ae-80e5-212a35d21961" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7358-9951-1e55d01572a0" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-79ae-80e5-212a35d21961" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-79ae-80e5-212a35d21961_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-79ae-80e5-212a35d21961" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-79ae-80e5-212a35d21961_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-71d3-b6a5-d573cd298706" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-79ae-80e5-212a35d21961" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-71d3-b6a5-d573cd298706" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-712e-b6ee-3e7125ed8096" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-71d3-b6a5-d573cd298706" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-712e-b6ee-3e7125ed8096" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DistributionInvestmentRider_019dd587-3b1f-7d3e-894c-edf1b1013f9b" xlink:href="dpl-20260331.xsd#dpl_DistributionInvestmentRider"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_DistributionInvestmentRider_019dd587-3b1f-7d3e-894c-edf1b1013f9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3b1f-7e8a-9cd3-239d69de001a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-3b1f-7e8a-9cd3-239d69de001a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-3b1f-7181-9069-42aa74b58dab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-3b1f-7181-9069-42aa74b58dab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Covid19DeferralWriteOff_019dd587-3b1f-78a7-a0d2-18b2ae4109da" xlink:href="dpl-20260331.xsd#dpl_Covid19DeferralWriteOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_Covid19DeferralWriteOff_019dd587-3b1f-78a7-a0d2-18b2ae4109da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-3b1f-7801-8bf6-5965bf8e884d" xlink:href="dpl-20260331.xsd#dpl_CostOfLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-3b1f-7801-8bf6-5965bf8e884d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-3b1f-7172-bd25-6c8d661406f0" xlink:href="dpl-20260331.xsd#dpl_RevenueIncreaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-3b1f-7172-bd25-6c8d661406f0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-3b1f-76d1-87d4-8f9e17ad0b84" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-3b1f-76d1-87d4-8f9e17ad0b84" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseDistributionRateCase_019dd587-3b1f-72cc-a356-0d429ca56bd1" xlink:href="dpl-20260331.xsd#dpl_RateBaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_RateBaseDistributionRateCase_019dd587-3b1f-72cc-a356-0d429ca56bd1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-3b1f-7593-aba2-35950376d68f" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-3b1f-7593-aba2-35950376d68f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-3b1f-756a-84b1-9d077a31c529" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-3b1f-756a-84b1-9d077a31c529" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityESP4_019dd587-3b1f-7c1e-95ec-b93d0efe376c" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_ReturnOnEquityESP4_019dd587-3b1f-7c1e-95ec-b93d0efe376c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RecoveryESP4_019dd587-3b1f-75ed-a554-d3feb28a4dd6" xlink:href="dpl-20260331.xsd#dpl_RecoveryESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_RecoveryESP4_019dd587-3b1f-75ed-a554-d3feb28a4dd6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferralOfPurchasedPowerCostsESP4_019dd587-3b1f-7f4f-8208-67337f82b33d" xlink:href="dpl-20260331.xsd#dpl_DeferralOfPurchasedPowerCostsESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_DeferralOfPurchasedPowerCostsESP4_019dd587-3b1f-7f4f-8208-67337f82b33d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferralOfCarryingCostsESP4_019dd587-3b1f-71de-baff-6571940c5db4" xlink:href="dpl-20260331.xsd#dpl_DeferralOfCarryingCostsESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7713-b420-85cf2505bd1c" xlink:to="loc_dpl_DeferralOfCarryingCostsESP4_019dd587-3b1f-71de-baff-6571940c5db4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-3b1f-757f-b23e-dd708c3294e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-3b1f-757f-b23e-dd708c3294e8" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c58-be68-1419f982830f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-3b1f-757f-b23e-dd708c3294e8" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7c58-be68-1419f982830f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7c58-be68-1419f982830f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-714d-9dda-691e33338ac7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-77c9-bd2e-1e88b9115a34" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-3b1f-757f-b23e-dd708c3294e8" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7eb9-a40e-f119784c58fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-710f-ae3e-2e8bf4e62d9e" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7eb9-a40e-f119784c58fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7293-8505-407d9468731c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7eb9-a40e-f119784c58fe" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7293-8505-407d9468731c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-3b1f-7f89-ba23-44963a44946b" xlink:href="dpl-20260331.xsd#dpl_RevenueIncreaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-3b1f-7f89-ba23-44963a44946b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-3b1f-70b7-a11b-8989a34d8b4d" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-3b1f-70b7-a11b-8989a34d8b4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-3b1f-78ae-9f55-f05e9c831e8e" xlink:href="dpl-20260331.xsd#dpl_CostOfLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-3b1f-78ae-9f55-f05e9c831e8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseDistributionRateCase_019dd587-3b1f-7f17-b6da-0fcc0a8895fb" xlink:href="dpl-20260331.xsd#dpl_RateBaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_RateBaseDistributionRateCase_019dd587-3b1f-7f17-b6da-0fcc0a8895fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-3b1f-73a0-8549-bb310ffd4a7e" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-3b1f-73a0-8549-bb310ffd4a7e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-3b1f-7e21-b253-0ff0f84c94cf" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-3b1f-7e21-b253-0ff0f84c94cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TFRTrueUpLiability_019dd587-3b1f-7448-830b-eefde42286cf" xlink:href="dpl-20260331.xsd#dpl_TFRTrueUpLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_TFRTrueUpLiability_019dd587-3b1f-7448-830b-eefde42286cf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TFRTrueUpLiabilityCurrent_019dd587-3b1f-76ca-955b-2b5a6d5c306a" xlink:href="dpl-20260331.xsd#dpl_TFRTrueUpLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_TFRTrueUpLiabilityCurrent_019dd587-3b1f-76ca-955b-2b5a6d5c306a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RSCRider_019dd587-3b1f-75a4-be84-ff663dd3bc9f" xlink:href="dpl-20260331.xsd#dpl_RSCRider"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_RSCRider_019dd587-3b1f-75a4-be84-ff663dd3bc9f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RecoveryESP4_019dd587-3b1f-74fa-b0b9-79b92dc0cbc3" xlink:href="dpl-20260331.xsd#dpl_RecoveryESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_RecoveryESP4_019dd587-3b1f-74fa-b0b9-79b92dc0cbc3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2Costs_019dd587-3b1f-70ae-a806-7f472e420015" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2Costs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_EstimatedSmartGridPhase2Costs_019dd587-3b1f-70ae-a806-7f472e420015" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2Capital_019dd587-3b1f-7c20-8356-a8a01cfbc67f" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2Capital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_EstimatedSmartGridPhase2Capital_019dd587-3b1f-7c20-8356-a8a01cfbc67f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2OM_019dd587-3b1f-74ba-a392-e48bcdb631f8" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2OM"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_EstimatedSmartGridPhase2OM_019dd587-3b1f-74ba-a392-e48bcdb631f8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NetCostDeferralDistributionRateCase_019dd587-3b1f-7577-93b7-45c1b1f9a614" xlink:href="dpl-20260331.xsd#dpl_NetCostDeferralDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_dpl_NetCostDeferralDistributionRateCase_019dd587-3b1f-7577-93b7-45c1b1f9a614" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilities_019dd587-3b1f-70bc-8359-8fc7ee8a7bbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-3b1f-7309-b389-7dbdac0b498c" xlink:to="loc_us-gaap_RegulatoryLiabilities_019dd587-3b1f-70bc-8359-8fc7ee8a7bbe" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-3b1f-7f7f-a2d2-bc9fe7af20ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-3b1f-7f7f-a2d2-bc9fe7af20ee" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-79bc-b3c0-8387242ae83c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-79bc-b3c0-8387242ae83c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-79bc-b3c0-8387242ae83c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-79bc-b3c0-8387242ae83c" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-79bc-b3c0-8387242ae83c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-7b25-a56d-dd6896715fef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-79bc-b3c0-8387242ae83c" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-7b25-a56d-dd6896715fef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7cdf-b5b3-7e86934fa42b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-7b25-a56d-dd6896715fef" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7cdf-b5b3-7e86934fa42b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-7c85-a840-3e2669499e8c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-7b25-a56d-dd6896715fef" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-7c85-a840-3e2669499e8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70b2-83ce-8149a9e067c4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70b2-83ce-8149a9e067c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70b2-83ce-8149a9e067c4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70b2-83ce-8149a9e067c4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70b2-83ce-8149a9e067c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-724c-8684-dbf850752564" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70b2-83ce-8149a9e067c4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-724c-8684-dbf850752564" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-70b5-a579-04920e39d0a2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-724c-8684-dbf850752564" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-70b5-a579-04920e39d0a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7e47-a4f2-81782ac3b864" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7e47-a4f2-81782ac3b864" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7e47-a4f2-81782ac3b864_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7e47-a4f2-81782ac3b864" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7e47-a4f2-81782ac3b864_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7fc3-b368-6abcf988840c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7e47-a4f2-81782ac3b864" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7fc3-b368-6abcf988840c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dd587-3b1f-72ca-9027-e390a2635249" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7fc3-b368-6abcf988840c" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dd587-3b1f-72ca-9027-e390a2635249" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dd587-3b1f-7961-be9b-88987e739dec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7fc3-b368-6abcf988840c" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dd587-3b1f-7961-be9b-88987e739dec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-7733-a1e1-5e82f1063cab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7fc3-b368-6abcf988840c" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-7733-a1e1-5e82f1063cab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7bbf-8ac2-8181859fe668" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7037-9bc7-5464cd3f3d8a" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7bbf-8ac2-8181859fe668" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7bbf-8ac2-8181859fe668_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7bbf-8ac2-8181859fe668" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7bbf-8ac2-8181859fe668_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7bbf-8ac2-8181859fe668" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-7117-886b-844327d756e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-7117-886b-844327d756e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-7997-88a9-164194212ffc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-7997-88a9-164194212ffc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-75c3-af2b-6ea9c8d8d0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-75c3-af2b-6ea9c8d8d0c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-3b1f-718d-a273-65a0d4934db6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b32-9c08-e3abd6384f87" xlink:to="loc_us-gaap_DebtMember_019dd587-3b1f-718d-a273-65a0d4934db6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72cb-9d85-7243ae2a318b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72cb-9d85-7243ae2a318b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70df-8b9e-83542c8d7167" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7356-9bb0-7315b0a33488" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-7fd2-b9f6-afa0c89b79fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-3b1f-7f7f-a2d2-bc9fe7af20ee" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-7fd2-b9f6-afa0c89b79fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-3b1f-72cc-8fdf-c473c03091fe" xlink:href="dpl-20260331.xsd#dpl_InvestmentsOtherThanDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-3b1f-7f7f-a2d2-bc9fe7af20ee" xlink:to="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-3b1f-72cc-8fdf-c473c03091fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-3b1f-742c-bdd1-197d8e752dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-3b1f-7f7f-a2d2-bc9fe7af20ee" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-3b1f-742c-bdd1-197d8e752dfa" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueandCostofNonDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueFairValueandCostofNonDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueFairValueandCostofNonDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e81-90ac-15bb1cd6acc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7d4c-a488-efde63474262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e81-90ac-15bb1cd6acc8" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7d4c-a488-efde63474262" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7b54-9d44-bef89c97df75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7d4c-a488-efde63474262" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7b54-9d44-bef89c97df75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b54-9d44-bef89c97df75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7b54-9d44-bef89c97df75" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7b54-9d44-bef89c97df75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-7b54-9d44-bef89c97df75" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-727b-b46b-82508b848758" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-727b-b46b-82508b848758" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-7a02-8110-1ce1e907a5ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-7a02-8110-1ce1e907a5ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-7993-b3b4-2b8c5b592d73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-7993-b3b4-2b8c5b592d73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-3b1f-7f9e-8dcf-a55f34cd3937" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-7832-8955-ef466a323be5" xlink:to="loc_us-gaap_DebtMember_019dd587-3b1f-7f9e-8dcf-a55f34cd3937" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-736a-bb7b-9926bb3769fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7d4c-a488-efde63474262" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-736a-bb7b-9926bb3769fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-736a-bb7b-9926bb3769fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-736a-bb7b-9926bb3769fb" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-736a-bb7b-9926bb3769fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-74e4-b081-4fda16e8fa59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-736a-bb7b-9926bb3769fb" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-74e4-b081-4fda16e8fa59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-706f-9fa6-e1c013c319f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-74e4-b081-4fda16e8fa59" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-706f-9fa6-e1c013c319f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dd587-3b1f-75e4-a50a-cc1387aaf001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-74e4-b081-4fda16e8fa59" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dd587-3b1f-75e4-a50a-cc1387aaf001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-757b-896c-42234ce27c67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-788f-b37c-1110954a9d3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-72f1-903a-284d259b6b3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-7284-b781-3495e961bb4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-74e4-b081-4fda16e8fa59" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-7284-b781-3495e961bb4f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74f0-9e5a-0e2402eda633" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-7d4c-a488-efde63474262" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74f0-9e5a-0e2402eda633" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-74f0-9e5a-0e2402eda633_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74f0-9e5a-0e2402eda633" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-74f0-9e5a-0e2402eda633_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7868-8763-f109e986d49c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-74f0-9e5a-0e2402eda633" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7868-8763-f109e986d49c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-75cd-9493-00c8393ea430" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7868-8763-f109e986d49c" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-75cd-9493-00c8393ea430" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-3b1f-743d-9dfd-cb74bc8b9219" xlink:href="dpl-20260331.xsd#dpl_InvestmentsOtherThanDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e81-90ac-15bb1cd6acc8" xlink:to="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-3b1f-743d-9dfd-cb74bc8b9219" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-3b1f-7864-aead-c72340346105" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e81-90ac-15bb1cd6acc8" xlink:to="loc_us-gaap_LongTermDebt_019dd587-3b1f-7864-aead-c72340346105" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-71bb-bcc4-afd5972b45de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e81-90ac-15bb1cd6acc8" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-71bb-bcc4-afd5972b45de" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-78b5-adcc-9cf145bb4525" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-78b5-adcc-9cf145bb4525" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-78b5-adcc-9cf145bb4525_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-78b5-adcc-9cf145bb4525" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-78b5-adcc-9cf145bb4525_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-3b1f-78b5-adcc-9cf145bb4525" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-75ef-b0a9-c06759dc8687" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-3b1f-75ef-b0a9-c06759dc8687" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-78af-b399-cbb6958eac07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-3b1f-78af-b399-cbb6958eac07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-7471-800a-a0ad2fecf08d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-3b1f-7471-800a-a0ad2fecf08d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-3b1f-723e-8362-733afc532c30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_DebtMember_019dd587-3b1f-723e-8362-733afc532c30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_019dd587-3b1f-7d29-ba5f-a777f68e2542" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_MutualFundMember_019dd587-3b1f-7d29-ba5f-a777f68e2542" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019ddb1d-8f4a-759f-87ed-edc3b0af7b11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-3b1f-753e-9078-efc845668c13" xlink:to="loc_us-gaap_LineOfCreditMember_019ddb1d-8f4a-759f-87ed-edc3b0af7b11" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-7bdc-b020-1eb144d3c3d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-7bdc-b020-1eb144d3c3d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7bdc-b020-1eb144d3c3d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-7bdc-b020-1eb144d3c3d5" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7bdc-b020-1eb144d3c3d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-76ae-8d46-7b46a39e226d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-3b1f-7bdc-b020-1eb144d3c3d5" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-76ae-8d46-7b46a39e226d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7ccb-8ce7-e6acc57b73f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-3b1f-76ae-8d46-7b46a39e226d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7ccb-8ce7-e6acc57b73f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7d29-89a0-5eb09434b163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-74a0-b218-c1d86655ecb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-3b1f-7d29-89a0-5eb09434b163" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-3b1f-74a0-b218-c1d86655ecb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7a04-a92f-0b9889540ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7a04-a92f-0b9889540ed3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7a04-a92f-0b9889540ed3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7a04-a92f-0b9889540ed3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-7a04-a92f-0b9889540ed3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-73d0-8df8-5dbaf90f20e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-7a04-a92f-0b9889540ed3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-73d0-8df8-5dbaf90f20e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dd587-3b1f-7a18-ac70-316063416cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-73d0-8df8-5dbaf90f20e1" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dd587-3b1f-7a18-ac70-316063416cdf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dd587-3b1f-75cf-8a08-97ae2f237dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-73d0-8df8-5dbaf90f20e1" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dd587-3b1f-75cf-8a08-97ae2f237dc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-7aac-8a1b-d97754128b79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-73d0-8df8-5dbaf90f20e1" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-7aac-8a1b-d97754128b79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7478-a0bd-2e7caf96c874" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ab6-9dfc-8f85e3a5e8c5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7478-a0bd-2e7caf96c874" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7b0d-bb93-68cb58cabe36" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7478-a0bd-2e7caf96c874" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7b0d-bb93-68cb58cabe36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-78e8-9557-ac0bb0a264ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-3b1f-71aa-bd78-aa4426197bcb" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-78e8-9557-ac0bb0a264ad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-78e8-9557-ac0bb0a264ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-78e8-9557-ac0bb0a264ad" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-78e8-9557-ac0bb0a264ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-77d4-9365-eb575613c506" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-78e8-9557-ac0bb0a264ad" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-77d4-9365-eb575613c506" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-7d23-a4d7-3793634b53e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-77d4-9365-eb575613c506" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-7d23-a4d7-3793634b53e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019dd587-3b1f-7dad-b8e2-c74912d18169" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019dd587-3b1f-7dad-b8e2-c74912d18169" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-7190-b1e7-12cb05acaeb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-3b1f-7190-b1e7-12cb05acaeb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019dd587-3b1f-7104-bd2e-7e021e0016a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019dd587-3b1f-7104-bd2e-7e021e0016a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-3b1f-713a-ac8b-e6b820d024b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7a84-ab30-10a92d4d0e55" xlink:to="loc_us-gaap_LongTermDebt_019dd587-3b1f-713a-ac8b-e6b820d024b9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueCashEquivalentsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueCashEquivalentsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueCashEquivalentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-762f-be0a-248da501adbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-7ada-87d1-aa0acea4be32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-762f-be0a-248da501adbf" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-7ada-87d1-aa0acea4be32" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ff5-b969-1c23bd76f9c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7ada-87d1-aa0acea4be32" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ff5-b969-1c23bd76f9c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ff5-b969-1c23bd76f9c7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ff5-b969-1c23bd76f9c7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ff5-b969-1c23bd76f9c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ed5-aad7-be4543406920" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ff5-b969-1c23bd76f9c7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ed5-aad7-be4543406920" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7c23-97fa-74815e8fad02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ed5-aad7-be4543406920" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7c23-97fa-74815e8fad02" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DerivativeInstrumentsandHedgingActivitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7c10-b4e3-9ad8a243960f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019dd587-3b1f-7699-b169-283682cd55ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7c10-b4e3-9ad8a243960f" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019dd587-3b1f-7699-b169-283682cd55ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-765e-b960-28a192f4d222" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019dd587-3b1f-7699-b169-283682cd55ff" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-765e-b960-28a192f4d222" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-765e-b960-28a192f4d222_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-765e-b960-28a192f4d222" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-765e-b960-28a192f4d222_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7077-bc56-a7df791d2654" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-765e-b960-28a192f4d222" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7077-bc56-a7df791d2654" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7073-9423-ab81aa84326a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7077-bc56-a7df791d2654" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7073-9423-ab81aa84326a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-78b5-bd58-bc0054fffc01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7c10-b4e3-9ad8a243960f" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-78b5-bd58-bc0054fffc01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019dd587-3b1f-7b0a-9842-f2dd25851246" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:to="loc_us-gaap_DerivativeTable_019dd587-3b1f-7b0a-9842-f2dd25851246" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7c5b-81c5-7eccd5458e0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019dd587-3b1f-7b0a-9842-f2dd25851246" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7c5b-81c5-7eccd5458e0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7c5b-81c5-7eccd5458e0c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7c5b-81c5-7eccd5458e0c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7c5b-81c5-7eccd5458e0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7278-960b-8dd79d3a7e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7c5b-81c5-7eccd5458e0c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7278-960b-8dd79d3a7e3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-7a7b-b8eb-394f576a7a5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7278-960b-8dd79d3a7e3e" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-7a7b-b8eb-394f576a7a5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7b4c-8368-4102ec89df76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019dd587-3b1f-7b0a-9842-f2dd25851246" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7b4c-8368-4102ec89df76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7b4c-8368-4102ec89df76_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7b4c-8368-4102ec89df76" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7b4c-8368-4102ec89df76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7177-b40a-24cd9e529e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7b4c-8368-4102ec89df76" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7177-b40a-24cd9e529e5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019dd587-3b1f-702b-8bf2-e83b10ef2fde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7177-b40a-24cd9e529e5c" xlink:to="loc_us-gaap_CashFlowHedgingMember_019dd587-3b1f-702b-8bf2-e83b10ef2fde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019dd587-3b1f-7650-b9dc-9fa074169444" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019dd587-3b1f-7650-b9dc-9fa074169444" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3b1f-7c38-9823-385740777f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3b1f-7c38-9823-385740777f9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_019dd587-3b1f-759a-a002-f716fcce1511" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:to="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_019dd587-3b1f-759a-a002-f716fcce1511" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3b1f-7f07-9013-819edd15202e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019dd587-3b1f-745b-9bf0-480aa83e05ff" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3b1f-7f07-9013-819edd15202e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesGainsorLossesRecognizedinAOCIfortheCashFlowHedgesDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DerivativeInstrumentsandHedgingActivitiesGainsorLossesRecognizedinAOCIfortheCashFlowHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DerivativeInstrumentsandHedgingActivitiesGainsorLossesRecognizedinAOCIfortheCashFlowHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e35-b011-4add9b2082f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019dd587-3b1f-72a8-9d04-3f05684c2f50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e35-b011-4add9b2082f2" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019dd587-3b1f-72a8-9d04-3f05684c2f50" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b16-8553-e4349db6fca6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019dd587-3b1f-72a8-9d04-3f05684c2f50" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b16-8553-e4349db6fca6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b16-8553-e4349db6fca6_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b16-8553-e4349db6fca6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b16-8553-e4349db6fca6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b14-b00e-5fedff81cba6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7b16-8553-e4349db6fca6" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b14-b00e-5fedff81cba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7176-a631-15e641945a36" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7b14-b00e-5fedff81cba6" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7176-a631-15e641945a36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7962-b4f3-043a411f79d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019dd587-3b1f-72a8-9d04-3f05684c2f50" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7962-b4f3-043a411f79d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7962-b4f3-043a411f79d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7962-b4f3-043a411f79d9" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7962-b4f3-043a411f79d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7db8-a65b-e7da019f5c73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-3b1f-7962-b4f3-043a411f79d9" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7db8-a65b-e7da019f5c73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-78d3-8cc0-0a7cd84eaa4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-3b1f-7db8-a65b-e7da019f5c73" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-78d3-8cc0-0a7cd84eaa4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-3b1f-7826-bbee-8089509f9a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AccumulatedDerivativeGainLossinAOCIRollForward_019dd587-3b1f-7114-a41a-fa026670e25a" xlink:href="dpl-20260331.xsd#dpl_AccumulatedDerivativeGainLossinAOCIRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e35-b011-4add9b2082f2" xlink:to="loc_dpl_AccumulatedDerivativeGainLossinAOCIRollForward_019dd587-3b1f-7114-a41a-fa026670e25a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019dd587-3b1f-7efb-9ab6-35ba154176f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_AccumulatedDerivativeGainLossinAOCIRollForward_019dd587-3b1f-7114-a41a-fa026670e25a" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_019dd587-3b1f-7efb-9ab6-35ba154176f1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7a44-b231-6213634c9ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7a44-b231-6213634c9ea3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7a44-b231-6213634c9ea3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7a44-b231-6213634c9ea3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7a44-b231-6213634c9ea3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7a44-b231-6213634c9ea3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-3b1f-7733-8a6d-d892a7e6946c" xlink:href="dpl-20260331.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-3b1f-7733-8a6d-d892a7e6946c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-3b1f-7f15-898b-38506a869135" xlink:href="dpl-20260331.xsd#dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-3b1f-7f15-898b-38506a869135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-3b1f-7164-b2e3-ec8bb8725c82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-3b1f-7164-b2e3-ec8bb8725c82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-3b1f-767f-a7bb-2d5ef7793e44" xlink:href="dpl-20260331.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-3b1f-767f-a7bb-2d5ef7793e44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-3b1f-7999-9eca-4ff91907a6e9" xlink:href="dpl-20260331.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-3b1f-7999-9eca-4ff91907a6e9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7312-9f8c-29dd9134508f" xlink:href="dpl-20260331.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7312-9f8c-29dd9134508f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7003-a403-b6812d9c2a87" xlink:href="dpl-20260331.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7003-a403-b6812d9c2a87" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7103-8c71-db098d3b5d3a" xlink:href="dpl-20260331.xsd#dpl_TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7103-8c71-db098d3b5d3a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FirstMortgageBondsDue2033Member_019dd587-3b1f-7ece-9e7c-315643ad1973" xlink:href="dpl-20260331.xsd#dpl_FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_FirstMortgageBondsDue2033Member_019dd587-3b1f-7ece-9e7c-315643ad1973" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-3b1f-7286-a682-56dd9195b132" xlink:href="dpl-20260331.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-3b1f-7286-a682-56dd9195b132" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-3b1f-72fc-8db2-84b1b5e70b1f" xlink:href="dpl-20260331.xsd#dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-3b1f-72fc-8db2-84b1b5e70b1f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-3b1f-7a1f-b691-4f6d12eb51bd" xlink:href="dpl-20260331.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-3b1f-7a1f-b691-4f6d12eb51bd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.35SeniorNotesdue2029Member_019ddb23-dbf2-75e8-bd20-77469c238423" xlink:href="dpl-20260331.xsd#dpl_A4.35SeniorNotesdue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7009-876b-3122173c5f0e" xlink:to="loc_dpl_A4.35SeniorNotesdue2029Member_019ddb23-dbf2-75e8-bd20-77469c238423" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ea4-adef-852a21f411ed" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ea4-adef-852a21f411ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ea4-adef-852a21f411ed_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ea4-adef-852a21f411ed" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ea4-adef-852a21f411ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-71f4-80a5-21bd62fa74a8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ea4-adef-852a21f411ed" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-71f4-80a5-21bd62fa74a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-744f-882f-caf7082e8ce3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-71f4-80a5-21bd62fa74a8" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-744f-882f-caf7082e8ce3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-7d47-b7b3-6ab923c6640b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-7d47-b7b3-6ab923c6640b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7d47-b7b3-6ab923c6640b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7d47-b7b3-6ab923c6640b" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7d47-b7b3-6ab923c6640b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-760b-a359-f114b5cf4871" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7d47-b7b3-6ab923c6640b" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-760b-a359-f114b5cf4871" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7124-be4b-bfa05fcfc7ca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-760b-a359-f114b5cf4871" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7124-be4b-bfa05fcfc7ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-7d7a-8eb4-cb91803cf640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-7d7a-8eb4-cb91803cf640" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7d7a-8eb4-cb91803cf640_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-7d7a-8eb4-cb91803cf640" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7d7a-8eb4-cb91803cf640_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7861-ad36-041d67d38fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-7d7a-8eb4-cb91803cf640" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7861-ad36-041d67d38fd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-7f06-b71b-0a4bf1d51436" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7861-ad36-041d67d38fd1" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-7f06-b71b-0a4bf1d51436" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019dd587-3b1f-76bb-9aea-41b5c38cdf45" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-77c2-81ff-86dab8a9e549" xlink:to="loc_srt_OwnershipAxis_019dd587-3b1f-76bb-9aea-41b5c38cdf45" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-3b1f-76bb-9aea-41b5c38cdf45_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019dd587-3b1f-76bb-9aea-41b5c38cdf45" xlink:to="loc_srt_OwnershipDomain_019dd587-3b1f-76bb-9aea-41b5c38cdf45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-3b1f-7b5b-a6e8-fd9c04464c59" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019dd587-3b1f-76bb-9aea-41b5c38cdf45" xlink:to="loc_srt_OwnershipDomain_019dd587-3b1f-7b5b-a6e8-fd9c04464c59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLOwnership_019dd587-3b1f-7967-ae89-de23bea35849" xlink:href="dpl-20260331.xsd#dpl_DPLOwnership"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-3b1f-7b5b-a6e8-fd9c04464c59" xlink:to="loc_dpl_DPLOwnership_019dd587-3b1f-7967-ae89-de23bea35849" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dd587-3b1f-7c24-97de-4bac541ec3d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_LineOfCredit_019dd587-3b1f-7c24-97de-4bac541ec3d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-7993-80c7-0d8d54f8db9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-7993-80c7-0d8d54f8db9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentNumberofFinancialCovenants_019dd587-3b1f-7c73-8b86-0872e2821b3a" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentNumberofFinancialCovenants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentNumberofFinancialCovenants_019dd587-3b1f-7c73-8b86-0872e2821b3a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters_019dd587-3b1f-72c8-a09d-d9d4df47824a" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters_019dd587-3b1f-72c8-a09d-d9d4df47824a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantDebttoEBITDARatioMaximum_019dd587-3b1f-7580-b82d-4239d5604e05" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantDebttoEBITDARatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtCovenantDebttoEBITDARatioMaximum_019dd587-3b1f-7580-b82d-4239d5604e05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantLeverageRatioMaximum_019dd587-3b1f-7ccd-b02c-8e0b4d4d0bb8" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtCovenantLeverageRatioMaximum_019dd587-3b1f-7ccd-b02c-8e0b4d4d0bb8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-3b1f-7cd3-bf0f-d9d5534473d9" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantInterestCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-3b1f-7cd3-bf0f-d9d5534473d9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-3b1f-7b49-94d2-903074021673" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-3b1f-7b49-94d2-903074021673" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3b1f-7d96-9658-efc398f017cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3b1f-7d96-9658-efc398f017cc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-3b1f-75e7-af1f-886970358a3d" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-3b1f-75e7-af1f-886970358a3d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-3b1f-7c11-be7f-2e62d358de52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-3b1f-7c11-be7f-2e62d358de52" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dd587-3b1f-78b3-8a16-ca62bfda59fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dd587-3b1f-78b3-8a16-ca62bfda59fd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-3b1f-75af-83d0-932eb8a851cc" xlink:href="dpl-20260331.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-3b1f-75af-83d0-932eb8a851cc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-3b1f-7c8d-827f-9017ff0749e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-3b1f-7c8d-827f-9017ff0749e6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit_019dd587-3b1f-7838-97a2-2c987ccb42a5" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit_019dd587-3b1f-7838-97a2-2c987ccb42a5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit_019dd587-3b1f-7802-9bfa-7d0456ea8fe4" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit_019dd587-3b1f-7802-9bfa-7d0456ea8fe4" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction_019dd587-3b1f-7e10-8ce3-ee9773823021" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction_019dd587-3b1f-7e10-8ce3-ee9773823021" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-3b1f-71b2-ab61-aba76eb2d773" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-3b1f-71b2-ab61-aba76eb2d773" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBankLoansAndNotesPayable_019dd587-3b1f-7d9d-b8b5-b1e7d98d49ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBankLoansAndNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_ShortTermBankLoansAndNotesPayable_019dd587-3b1f-7d9d-b8b5-b1e7d98d49ef" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dd587-3b1f-778a-8362-efb64a12d508" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dd587-3b1f-778a-8362-efb64a12d508" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-3b1f-702f-8121-4c84a34856b0" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-3b1f-702f-8121-4c84a34856b0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3b1f-737c-8a32-b8ec6ddab273" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-3b1f-737c-8a32-b8ec6ddab273" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UncommittedAccordionFeature_019dd587-3b1f-7881-a095-095594e3b668" xlink:href="dpl-20260331.xsd#dpl_UncommittedAccordionFeature"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-70ef-aca5-5e5d7e6704bc" xlink:to="loc_dpl_UncommittedAccordionFeature_019dd587-3b1f-7881-a095-095594e3b668" xlink:type="arc" order="22"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtLongtermDebtDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtLongtermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtLongtermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-7817-bd06-a554b56a145b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-7817-bd06-a554b56a145b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7170-a684-302b360e054c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-7817-bd06-a554b56a145b" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7170-a684-302b360e054c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7170-a684-302b360e054c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7170-a684-302b360e054c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7170-a684-302b360e054c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7170-a684-302b360e054c" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-3b1f-71cb-bd18-a5bd8e607045" xlink:href="dpl-20260331.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-3b1f-71cb-bd18-a5bd8e607045" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-3b1f-73f3-9f47-e7ea4077e8aa" xlink:href="dpl-20260331.xsd#dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-3b1f-73f3-9f47-e7ea4077e8aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-3b1f-719e-9977-8121384921c8" xlink:href="dpl-20260331.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-3b1f-719e-9977-8121384921c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.35SeniorNotesdue2029Member_019dd587-3b1f-71e8-87b2-b34f53103251" xlink:href="dpl-20260331.xsd#dpl_A4.35SeniorNotesdue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A4.35SeniorNotesdue2029Member_019dd587-3b1f-71e8-87b2-b34f53103251" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember_019dd587-3b1f-7f09-b6c0-71a172c85203" xlink:href="dpl-20260331.xsd#dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember_019dd587-3b1f-7f09-b6c0-71a172c85203" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A413SeniorNotesDue2025Member_019dd587-3b1f-7a7c-8dad-c7bd5ed9c45f" xlink:href="dpl-20260331.xsd#dpl_A413SeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A413SeniorNotesDue2025Member_019dd587-3b1f-7a7c-8dad-c7bd5ed9c45f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-3b1f-7cb0-baff-85b70bcd8541" xlink:href="dpl-20260331.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-3b1f-7cb0-baff-85b70bcd8541" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7344-a283-dbcd415da757" xlink:href="dpl-20260331.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-7344-a283-dbcd415da757" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-746e-94a9-a65a472e403d" xlink:href="dpl-20260331.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-3b1f-746e-94a9-a65a472e403d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-3b1f-7c66-8061-3e9b3ca71888" xlink:href="dpl-20260331.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-3b1f-7c66-8061-3e9b3ca71888" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70SeniorNotesDue2033Member_019dd587-3b1f-735f-8673-efa7518c9a46" xlink:href="dpl-20260331.xsd#dpl_A5.70SeniorNotesDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A5.70SeniorNotesDue2033Member_019dd587-3b1f-735f-8673-efa7518c9a46" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-3b1f-7d32-b4e1-662628e506b8" xlink:href="dpl-20260331.xsd#dpl_A5.49SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-3b1f-7d32-b4e1-662628e506b8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-3b1f-768a-9368-7574b96e0849" xlink:href="dpl-20260331.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-3b1f-768a-9368-7574b96e0849" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-3b1f-75ce-b950-c701c65532f5" xlink:href="dpl-20260331.xsd#dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-3b1f-75ce-b950-c701c65532f5" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-3b1f-7b2e-8d3c-30fd67f9ef2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-3b1f-7b2e-8d3c-30fd67f9ef2b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.55FirstMortgageBondsDue2030Member_019dd587-3b1f-7aa6-95d8-f7b3d2e1f28c" xlink:href="dpl-20260331.xsd#dpl_A4.55FirstMortgageBondsDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-775b-8404-1424a393fe82" xlink:to="loc_dpl_A4.55FirstMortgageBondsDue2030Member_019dd587-3b1f-7aa6-95d8-f7b3d2e1f28c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75c1-883a-083dbd6a5405" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-7817-bd06-a554b56a145b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75c1-883a-083dbd6a5405" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-75c1-883a-083dbd6a5405_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75c1-883a-083dbd6a5405" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-75c1-883a-083dbd6a5405_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fbe-a774-28a77860e0bd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-75c1-883a-083dbd6a5405" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fbe-a774-28a77860e0bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-73ca-856e-11dd84cd67a0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fbe-a774-28a77860e0bd" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-73ca-856e-11dd84cd67a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7d5b-acc5-b207ba1410c1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-79b1-9e93-81dfba32ba49" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-3b1f-7817-bd06-a554b56a145b" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-79b1-9e93-81dfba32ba49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-79b1-9e93-81dfba32ba49_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-79b1-9e93-81dfba32ba49" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-79b1-9e93-81dfba32ba49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-76e2-a55a-7aa913a4fdfa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-79b1-9e93-81dfba32ba49" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-76e2-a55a-7aa913a4fdfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7447-a2a0-bd484110538d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-76e2-a55a-7aa913a4fdfa" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7447-a2a0-bd484110538d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-3b1f-7b30-b090-79cfdc58c363" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-3b1f-7b30-b090-79cfdc58c363" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-3b1f-71e3-a7c2-c1233347c309" xlink:href="dpl-20260331.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-3b1f-71e3-a7c2-c1233347c309" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019dd587-3b1f-791f-a509-0fe937531276" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019dd587-3b1f-791f-a509-0fe937531276" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-3b1f-7468-ba65-cf60ef675704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-3b1f-7468-ba65-cf60ef675704" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments_019dd587-3b1f-72a6-b5cf-4147cda453b1" xlink:href="dpl-20260331.xsd#dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments_019dd587-3b1f-72a6-b5cf-4147cda453b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-3b1f-7550-a5bc-6295c2cad0c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_LongTermDebt_019dd587-3b1f-7550-a5bc-6295c2cad0c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dd587-3b1f-702f-8170-22ce40d4469d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dd587-3b1f-702f-8170-22ce40d4469d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3b1f-715b-a4bf-c2205451cfb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-3b1f-715b-a4bf-c2205451cfb5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-3b1f-7b02-b094-248c57a85af0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-3b1f-7b02-b094-248c57a85af0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-3b1f-74e5-b4ed-e467d9eacc0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-3b1f-74e5-b4ed-e467d9eacc0e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dd587-3b1f-7827-86d3-2d9b14c4c3cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_LineOfCredit_019dd587-3b1f-7827-86d3-2d9b14c4c3cf" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-3b1f-72f0-a875-a81ebbba5d01" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantInterestCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-3b1f-72f0-a875-a81ebbba5d01" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-3b1f-7b6e-ab8b-b116f7c5f408" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-3b1f-7b6e-ab8b-b116f7c5f408" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3b1f-743a-a9c6-4645d2dcb149" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-3b1f-743a-a9c6-4645d2dcb149" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-7424-bf03-b130d7cb7584" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-3b1f-7424-bf03-b130d7cb7584" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UncommittedAccordionFeature_019dd587-3b1f-7dee-8e6d-e57dcb97a77b" xlink:href="dpl-20260331.xsd#dpl_UncommittedAccordionFeature"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_UncommittedAccordionFeature_019dd587-3b1f-7dee-8e6d-e57dcb97a77b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-3b1f-7d7d-a541-cb549fe203be" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-3b1f-7dc8-b5aa-b792c74e77bf" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-3b1f-7d7d-a541-cb549fe203be" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-3b1f-7a52-8892-fbef48fdb9f0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_dei_EntitiesTable_019dd587-3b1f-7a52-8892-fbef48fdb9f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-737d-ac98-4aa531c6c558" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-3b1f-7a52-8892-fbef48fdb9f0" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-737d-ac98-4aa531c6c558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-737d-ac98-4aa531c6c558_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-737d-ac98-4aa531c6c558" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-737d-ac98-4aa531c6c558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77bf-9a3b-ee2e3ee0cdea" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-737d-ac98-4aa531c6c558" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77bf-9a3b-ee2e3ee0cdea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7015-a32c-432eacfa5db8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77bf-9a3b-ee2e3ee0cdea" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7015-a32c-432eacfa5db8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-7897-8089-0b49a3d1b8af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-7897-8089-0b49a3d1b8af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-723d-b2a5-ef7b9ec7dab4" xlink:href="dpl-20260331.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-723d-b2a5-ef7b9ec7dab4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent_019dd587-3b1f-7ad4-a987-08e18245afdb" xlink:href="dpl-20260331.xsd#dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent_019dd587-3b1f-7ad4-a987-08e18245afdb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019dd587-3b1f-7878-8285-fc21f23c27f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019dd587-3b1f-7878-8285-fc21f23c27f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3b1f-7532-9385-889b08b03ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-3b1f-7532-9385-889b08b03ae0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TransferOfNetTaxLiability_019dd587-3b1f-79be-a76b-635254528a96" xlink:href="dpl-20260331.xsd#dpl_TransferOfNetTaxLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-3b1f-7cfd-83fc-33b318b9cd94" xlink:to="loc_dpl_TransferOfNetTaxLiability_019dd587-3b1f-79be-a76b-635254528a96" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-3b1f-75c6-8cbe-7a0783d88a45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019dd587-3b1f-7abd-8339-df4a5803e63a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-3b1f-75c6-8cbe-7a0783d88a45" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019dd587-3b1f-7abd-8339-df4a5803e63a" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-7a96-bffd-59a012edcbc3" xlink:href="dpl-20260331.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-3b1f-75c6-8cbe-7a0783d88a45" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-3b1f-7a96-bffd-59a012edcbc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3b1f-7760-b92a-4fb9d2756494" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-3b1f-75c6-8cbe-7a0783d88a45" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-3b1f-7760-b92a-4fb9d2756494" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInformationPertainingToIncomeTaxes_019dd587-3b1f-767d-86ba-d1401115c1e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInformationPertainingToIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-3b1f-75c6-8cbe-7a0783d88a45" xlink:to="loc_us-gaap_OtherInformationPertainingToIncomeTaxes_019dd587-3b1f-767d-86ba-d1401115c1e9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansNetPeriodicBenefitCostIncomeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansNetPeriodicBenefitCostIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansNetPeriodicBenefitCostIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7916-b9ae-ff77a5bf3d03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7916-b9ae-ff77a5bf3d03" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7946-a20f-fbd08f77737c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7916-b9ae-ff77a5bf3d03" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7946-a20f-fbd08f77737c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7946-a20f-fbd08f77737c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7946-a20f-fbd08f77737c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7946-a20f-fbd08f77737c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e1f-9b79-66539d5def9a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7946-a20f-fbd08f77737c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e1f-9b79-66539d5def9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-70c8-a3d0-641951ab8e61" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e1f-9b79-66539d5def9a" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-70c8-a3d0-641951ab8e61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7543-ad5e-ee3cc49e106e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7916-b9ae-ff77a5bf3d03" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7543-ad5e-ee3cc49e106e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7543-ad5e-ee3cc49e106e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7543-ad5e-ee3cc49e106e" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7543-ad5e-ee3cc49e106e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7ee6-9779-e1e509db832c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7543-ad5e-ee3cc49e106e" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7ee6-9779-e1e509db832c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-770d-b97f-e9f50c851f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7ee6-9779-e1e509db832c" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-770d-b97f-e9f50c851f7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-3b1f-7170-959e-df90c98aa653" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7ee6-9779-e1e509db832c" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-3b1f-7170-959e-df90c98aa653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019dd587-3b1f-7397-bb0c-4c9879cf5ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019dd587-3b1f-7397-bb0c-4c9879cf5ef9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_019dd587-3b1f-795a-81c9-6aa389009b46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_019dd587-3b1f-795a-81c9-6aa389009b46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_019dd587-3b1f-73be-85da-3c2f1593e67f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_019dd587-3b1f-73be-85da-3c2f1593e67f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019dd587-3b1f-7683-8321-8b98dce4a6f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019dd587-3b1f-7683-8321-8b98dce4a6f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019dd587-3b1f-7741-83e7-79fa037377d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019dd587-3b1f-7741-83e7-79fa037377d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019dd587-3b1f-708c-84b3-7453016b8e78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019dd587-3b1f-708c-84b3-7453016b8e78" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019dd587-3b1f-7c8c-8f7c-5af3473110f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019dd587-3b1f-7c8c-8f7c-5af3473110f1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-3b1f-796c-9fa9-ccc7cd9fb60f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-73f7-b741-3b96e5370220" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-3b1f-796c-9fa9-ccc7cd9fb60f" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7b09-8fb9-076a28eec922" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7b25-a9ce-652e34f82cc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7b09-8fb9-076a28eec922" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7b25-a9ce-652e34f82cc5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7b25-a9ce-652e34f82cc5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a8b-ae9f-55993d3a4f04" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7254-b5ea-ffc37f8e6ec5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a8b-ae9f-55993d3a4f04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7f03-b9ce-3a67fec43007" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7a8b-ae9f-55993d3a4f04" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7f03-b9ce-3a67fec43007" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7c1f-b47d-7c40c0684ff7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-3b1f-7b25-a9ce-652e34f82cc5" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7c1f-b47d-7c40c0684ff7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7c1f-b47d-7c40c0684ff7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7c1f-b47d-7c40c0684ff7" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7c1f-b47d-7c40c0684ff7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7d8f-b5fb-d6ebb19269a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-3b1f-7c1f-b47d-7c40c0684ff7" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7d8f-b5fb-d6ebb19269a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-76a8-ba79-5ee0c6603d70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7d8f-b5fb-d6ebb19269a3" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-3b1f-76a8-ba79-5ee0c6603d70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-3b1f-742f-b9e9-4c57956f5538" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-3b1f-7d8f-b5fb-d6ebb19269a3" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-3b1f-742f-b9e9-4c57956f5538" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-3b1f-7acd-8d40-4bc00a26c9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7b09-8fb9-076a28eec922" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-3b1f-7acd-8d40-4bc00a26c9ff" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/EquityDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#EquityDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/EquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-715f-ab79-88219f80d055" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-715f-ab79-88219f80d055" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-715f-ab79-88219f80d055_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-715f-ab79-88219f80d055" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-715f-ab79-88219f80d055_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7cbb-8491-affbecd7e077" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-3b1f-715f-ab79-88219f80d055" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7cbb-8491-affbecd7e077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-784a-b7c8-d460966cb1f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-3b1f-7cbb-8491-affbecd7e077" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-3b1f-784a-b7c8-d460966cb1f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7417-96f3-ea1c03129f10" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7417-96f3-ea1c03129f10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7417-96f3-ea1c03129f10_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7417-96f3-ea1c03129f10" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7417-96f3-ea1c03129f10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7443-87eb-a93aa7ec13ee" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7417-96f3-ea1c03129f10" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7443-87eb-a93aa7ec13ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-77aa-80a5-99f1f8dbc7d6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7443-87eb-a93aa7ec13ee" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-77aa-80a5-99f1f8dbc7d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLMember_019de447-9b9e-7c60-864f-5d1e8a5ec715" xlink:href="dpl-20260331.xsd#dpl_DPLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7443-87eb-a93aa7ec13ee" xlink:to="loc_dpl_DPLMember_019de447-9b9e-7c60-864f-5d1e8a5ec715" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-755a-afd7-ea7d5247f0f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-755a-afd7-ea7d5247f0f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-755a-afd7-ea7d5247f0f0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-755a-afd7-ea7d5247f0f0" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-755a-afd7-ea7d5247f0f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7210-ba96-ac7810b4c3f4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-755a-afd7-ea7d5247f0f0" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7210-ba96-ac7810b4c3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7ab3-8074-eeb02a4ec1aa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7210-ba96-ac7810b4c3f4" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7ab3-8074-eeb02a4ec1aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3b1f-7ddb-85a8-a2fcac04f499" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3b1f-7ddb-85a8-a2fcac04f499" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7ddb-85a8-a2fcac04f499_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3b1f-7ddb-85a8-a2fcac04f499" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7ddb-85a8-a2fcac04f499_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-3b1f-7ddb-85a8-a2fcac04f499" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3b1f-7855-a0e5-520b43cde25b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAdditionalCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-3b1f-7855-a0e5-520b43cde25b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dd587-3b1f-7e2c-9bd9-bb479096a0e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:to="loc_us-gaap_CommonStockMember_019dd587-3b1f-7e2c-9bd9-bb479096a0e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3b1f-7f3d-97b3-99fe648c33aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019dd587-3b1f-7f3d-97b3-99fe648c33aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3b1f-7518-8c9f-1e41f3962657" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-3b1f-7328-95a7-d5aeccea2ee7" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-3b1f-7518-8c9f-1e41f3962657" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dd587-3b1f-7ebe-8c8e-11203076914e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_dei_LegalEntityAxis_019dd587-3b1f-7ebe-8c8e-11203076914e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-3b1f-7ebe-8c8e-11203076914e_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dd587-3b1f-7ebe-8c8e-11203076914e" xlink:to="loc_dei_EntityDomain_019dd587-3b1f-7ebe-8c8e-11203076914e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-3b1f-7cae-99a9-8fcf3835eaee" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dd587-3b1f-7ebe-8c8e-11203076914e" xlink:to="loc_dei_EntityDomain_019dd587-3b1f-7cae-99a9-8fcf3835eaee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLMember_019dd587-3b1f-7628-8dc9-f46bb35e2959" xlink:href="dpl-20260331.xsd#dpl_DPLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3b1f-7cae-99a9-8fcf3835eaee" xlink:to="loc_dpl_DPLMember_019dd587-3b1f-7628-8dc9-f46bb35e2959" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQMember_019dd587-3b1f-7f48-bc68-dec16a44c819" xlink:href="dpl-20260331.xsd#dpl_CDPQMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3b1f-7cae-99a9-8fcf3835eaee" xlink:to="loc_dpl_CDPQMember_019dd587-3b1f-7f48-bc68-dec16a44c819" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsMember_019dd587-3b1f-79d5-bcd1-a1a2c5161a09" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-3b1f-7cae-99a9-8fcf3835eaee" xlink:to="loc_dpl_OhioHoldingsMember_019dd587-3b1f-79d5-bcd1-a1a2c5161a09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-72b5-be1e-1342317136fa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-72b5-be1e-1342317136fa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-72b5-be1e-1342317136fa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-72b5-be1e-1342317136fa" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-72b5-be1e-1342317136fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7155-99a0-f4382a982963" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-72b5-be1e-1342317136fa" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7155-99a0-f4382a982963" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-7515-9518-51d2c78f684c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7155-99a0-f4382a982963" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-7515-9518-51d2c78f684c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7047-ba57-742a63371895" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7047-ba57-742a63371895" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7047-ba57-742a63371895_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7047-ba57-742a63371895" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7047-ba57-742a63371895_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7e59-9b16-41234a3e2c93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7047-ba57-742a63371895" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7e59-9b16-41234a3e2c93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3b1f-7df8-85cb-31e6a5827d5a" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-7e59-9b16-41234a3e2c93" xlink:to="loc_dpl_UtilityMember_019dd587-3b1f-7df8-85cb-31e6a5827d5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7fee-8202-4451920b8c5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7fee-8202-4451920b8c5d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7fee-8202-4451920b8c5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7fee-8202-4451920b8c5d" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-7fee-8202-4451920b8c5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-730a-ad0c-a56b407a341f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConversionOfStockNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_019dd587-3b1f-7fee-8202-4451920b8c5d" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-730a-ad0c-a56b407a341f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dd587-3b1f-7291-b531-af5025b97cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-730a-ad0c-a56b407a341f" xlink:to="loc_us-gaap_CommonStockMember_019dd587-3b1f-7291-b531-af5025b97cb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMember_019dd587-3b1f-7f37-92a2-55e3187c6a7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_019dd587-3b1f-730a-ad0c-a56b407a341f" xlink:to="loc_us-gaap_EquityMember_019dd587-3b1f-7f37-92a2-55e3187c6a7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3b1f-7175-bf14-870bc5058e13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3b1f-7175-bf14-870bc5058e13" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7175-bf14-870bc5058e13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3b1f-7175-bf14-870bc5058e13" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7175-bf14-870bc5058e13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7724-b625-842cb9264d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019dd587-3b1f-7175-bf14-870bc5058e13" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7724-b625-842cb9264d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMember_019dd587-3b1f-7005-9725-fd3d1d9e789c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7724-b625-842cb9264d1d" xlink:to="loc_us-gaap_EquityMember_019dd587-3b1f-7005-9725-fd3d1d9e789c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3b1f-71d4-bd01-85e7df49b58c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019dd587-3b1f-7724-b625-842cb9264d1d" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-3b1f-71d4-bd01-85e7df49b58c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de01b-efdf-70e5-8e77-be849b33eaa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7e57-b8ce-7e9109311f89" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de01b-efdf-70e5-8e77-be849b33eaa6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-70e5-8e77-be849b33eaa6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de01b-efdf-70e5-8e77-be849b33eaa6" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-70e5-8e77-be849b33eaa6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-790e-aaca-34816a72ca34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019de01b-efdf-70e5-8e77-be849b33eaa6" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-790e-aaca-34816a72ca34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019de01c-0a63-7baf-a525-ee0f51595b8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-790e-aaca-34816a72ca34" xlink:to="loc_us-gaap_CashFlowHedgingMember_019de01c-0a63-7baf-a525-ee0f51595b8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOtherMember_019de01c-926e-7113-b254-aa85190a5539" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-790e-aaca-34816a72ca34" xlink:to="loc_us-gaap_ReclassificationOtherMember_019de01c-926e-7113-b254-aa85190a5539" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfundedPlanMember_019de454-5f3d-7101-8e4b-bd6574fb4240" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnfundedPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019de01b-efdf-790e-aaca-34816a72ca34" xlink:to="loc_us-gaap_UnfundedPlanMember_019de454-5f3d-7101-8e4b-bd6574fb4240" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_019dd587-3b1f-78cb-af8b-b66f210fb7c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_019dd587-3b1f-78cb-af8b-b66f210fb7c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CashContributionFromParentCompany_019dd587-3b1f-7b19-81d8-6a6572e0b442" xlink:href="dpl-20260331.xsd#dpl_CashContributionFromParentCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_CashContributionFromParentCompany_019dd587-3b1f-7b19-81d8-6a6572e0b442" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3b1f-7ef3-8be1-09a7ba63ba52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-3b1f-7ef3-8be1-09a7ba63ba52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_019dd587-3b1f-766c-a67c-26b13c72c8d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfRedeemableConvertiblePreferredStock_019dd587-3b1f-766c-a67c-26b13c72c8d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Noncashcapitalcontribution_019dd587-3b1f-7839-8b92-3a83d7c4a826" xlink:href="dpl-20260331.xsd#dpl_Noncashcapitalcontribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_Noncashcapitalcontribution_019dd587-3b1f-7839-8b92-3a83d7c4a826" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PaymentAgainstTaxReceivableBalanceFromParent_019dd587-3b1f-7709-b093-e108c6d83911" xlink:href="dpl-20260331.xsd#dpl_PaymentAgainstTaxReceivableBalanceFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_PaymentAgainstTaxReceivableBalanceFromParent_019dd587-3b1f-7709-b093-e108c6d83911" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dd587-3b1f-7d2b-9eb8-ee3025184027" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_StockholdersEquityOther_019dd587-3b1f-7d2b-9eb8-ee3025184027" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityCapitalContributionsReceived_019dd587-3b1f-711a-8880-43a2c3eba0af" xlink:href="dpl-20260331.xsd#dpl_EquityCapitalContributionsReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_EquityCapitalContributionsReceived_019dd587-3b1f-711a-8880-43a2c3eba0af" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralPartnersContributedCapital_019dd587-3b1f-70a2-b340-7c9cc27440bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralPartnersContributedCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_GeneralPartnersContributedCapital_019dd587-3b1f-70a2-b340-7c9cc27440bd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3b1f-794b-8960-7466295fcafb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-3b1f-794b-8960-7466295fcafb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquity_019dd587-3b1f-75a4-abab-9c9b01bc8b1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MembersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_MembersEquity_019dd587-3b1f-75a4-abab-9c9b01bc8b1d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019dd587-3b1f-7b34-ae9f-6ae21861b545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019dd587-3b1f-7b34-ae9f-6ae21861b545" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3b1f-76fa-9acd-ddb8717c62d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-3b1f-76fa-9acd-ddb8717c62d2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dd587-3b1f-7ecc-ad37-fcb90a8dd6e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019dd587-3b1f-7ecc-ad37-fcb90a8dd6e4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentTotal_019dd587-3b1f-74e2-b598-b84a01c51c47" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_CDPQInvestmentTotal_019dd587-3b1f-74e2-b598-b84a01c51c47" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMinorityShareholders_019dd587-3b1f-7160-b656-1e8e73ad0f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromMinorityShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_ProceedsFromMinorityShareholders_019dd587-3b1f-7160-b656-1e8e73ad0f38" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_019dd587-3b1f-7857-bb0b-ecb356accf26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalOther_019dd587-3b1f-7857-bb0b-ecb356accf26" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-3b1f-7fad-aaff-388d90c98f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-3b1f-7fad-aaff-388d90c98f1a" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3b1f-7421-aef8-d39c352b30c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_019dd587-3b1f-7421-aef8-d39c352b30c2" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3b1f-713a-8ace-3f75dc131b77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_019dd587-3b1f-713a-8ace-3f75dc131b77" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3b1f-77b0-8a62-1609ef1bc874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_019dd587-3b1f-77b0-8a62-1609ef1bc874" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019dd587-3b1f-7b91-bb90-9daa62ae2062" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_SharesIssued_019dd587-3b1f-7b91-bb90-9daa62ae2062" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentPercent_019dd587-3b1f-7994-a093-a4ad51834a8f" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_CDPQInvestmentPercent_019dd587-3b1f-7994-a093-a4ad51834a8f" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3b1f-7bca-8150-fca692ef7daa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-3b1f-7bca-8150-fca692ef7daa" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-3b1f-7616-8308-f40cd7a353b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-3b1f-7616-8308-f40cd7a353b5" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3b1f-7aa0-b7f5-e66b73e69d88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-3b1f-7aa0-b7f5-e66b73e69d88" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019dd587-3b1f-7f9f-9d91-8a88a20d0398" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019dd587-3b1f-7f9f-9d91-8a88a20d0398" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019de44f-06e1-7a4e-92b5-0b2eb9910f57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019de44f-06e1-7a4e-92b5-0b2eb9910f57" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityContributionFromParent_019ddfee-2a6b-706f-b51b-3964f7f4bcc5" xlink:href="dpl-20260331.xsd#dpl_EquityContributionFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_dpl_EquityContributionFromParent_019ddfee-2a6b-706f-b51b-3964f7f4bcc5" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_019de44d-cec4-72a2-908a-aea469161f77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax_019de44d-cec4-72a2-908a-aea469161f77" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019de450-9ded-7332-a4a7-b855d957e5bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7e04-ae0c-f09dc6b113fc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019de450-9ded-7332-a4a7-b855d957e5bb" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:to="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-3b1f-71bc-8967-cbee8657b910" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-3b1f-71bc-8967-cbee8657b910" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019dd587-3b1f-71bc-8967-cbee8657b910_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-3b1f-71bc-8967-cbee8657b910" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019dd587-3b1f-71bc-8967-cbee8657b910_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019dd587-3b1f-75ad-8305-83c4724e5129" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-3b1f-71bc-8967-cbee8657b910" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019dd587-3b1f-75ad-8305-83c4724e5129" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricGenerationCompanyMember_019dd587-3b1f-78c4-bfbf-bc47a520223f" xlink:href="dpl-20260331.xsd#dpl_ElectricGenerationCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019dd587-3b1f-75ad-8305-83c4724e5129" xlink:to="loc_dpl_ElectricGenerationCompanyMember_019dd587-3b1f-78c4-bfbf-bc47a520223f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7115-8716-e44a86bfcc37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7115-8716-e44a86bfcc37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7115-8716-e44a86bfcc37_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7115-8716-e44a86bfcc37" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-7115-8716-e44a86bfcc37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-79ab-a3eb-b45405aca661" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-3b1f-7115-8716-e44a86bfcc37" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-79ab-a3eb-b45405aca661" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtObligationOn49EquityOwnershipMember_019dd587-3b1f-7e43-b9ac-67ad940be99a" xlink:href="dpl-20260331.xsd#dpl_DebtObligationOn49EquityOwnershipMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-3b1f-79ab-a3eb-b45405aca661" xlink:to="loc_dpl_DebtObligationOn49EquityOwnershipMember_019dd587-3b1f-7e43-b9ac-67ad940be99a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-782a-9ab1-a673ae973eea" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7ecf-a4cf-4a85b6c1d68e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-782a-9ab1-a673ae973eea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7325-bbe1-9ccb23296f90" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-782a-9ab1-a673ae973eea" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7325-bbe1-9ccb23296f90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis_019dd587-3b1f-7415-aadf-9f254236fec3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis_019dd587-3b1f-7415-aadf-9f254236fec3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain_019dd587-3b1f-7415-aadf-9f254236fec3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis_019dd587-3b1f-7415-aadf-9f254236fec3" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain_019dd587-3b1f-7415-aadf-9f254236fec3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain_019dd587-3b1f-71e8-849f-aefaa4034b4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAxis_019dd587-3b1f-7415-aadf-9f254236fec3" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsDomain_019dd587-3b1f-71e8-849f-aefaa4034b4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019dd587-3b1f-77fe-95bb-bef5d3c520f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-3b1f-738f-9159-76d630459b37" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019dd587-3b1f-77fe-95bb-bef5d3c520f6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-77fe-95bb-bef5d3c520f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dd587-3b1f-77fe-95bb-bef5d3c520f6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-77fe-95bb-bef5d3c520f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-7ee2-a20a-8d20b6e948bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dd587-3b1f-77fe-95bb-bef5d3c520f6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-7ee2-a20a-8d20b6e948bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQMember_019dd587-3b1f-7e1f-85ff-365ec9ba651b" xlink:href="dpl-20260331.xsd#dpl_CDPQMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-7ee2-a20a-8d20b6e948bc" xlink:to="loc_dpl_CDPQMember_019dd587-3b1f-7e1f-85ff-365ec9ba651b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3b1f-7272-ab82-53c9049ac3b0" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dd587-3b1f-7ee2-a20a-8d20b6e948bc" xlink:to="loc_dpl_UtilityMember_019dd587-3b1f-7272-ab82-53c9049ac3b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_019dd587-3b1f-7743-af5b-3f0099b50a7c" xlink:href="dpl-20260331.xsd#dpl_PublicUtilitiesEquityInterestCostMethodPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:to="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_019dd587-3b1f-7743-af5b-3f0099b50a7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_019dd587-3b1f-7dda-905d-529eeefcf108" xlink:href="dpl-20260331.xsd#dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:to="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_019dd587-3b1f-7dda-905d-529eeefcf108" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019dd587-3b1f-7eee-86a1-3de7a9499331" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019dd587-3b1f-7eee-86a1-3de7a9499331" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019dd587-3b1f-7910-9cf9-26f5cd2f19fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-3b1f-7813-a3b6-b6ef2afc85fe" xlink:to="loc_us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_019dd587-3b1f-7910-9cf9-26f5cd2f19fe" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7249-9a40-b2500c6e0e94" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7249-9a40-b2500c6e0e94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7249-9a40-b2500c6e0e94_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7249-9a40-b2500c6e0e94" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7249-9a40-b2500c6e0e94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7b33-a5ce-84153963ef20" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-7249-9a40-b2500c6e0e94" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7b33-a5ce-84153963ef20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-7d7e-8433-9fa162868226" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7b33-a5ce-84153963ef20" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-7d7e-8433-9fa162868226" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019dd587-3b1f-787e-82c3-6d897f549f6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7b33-a5ce-84153963ef20" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019dd587-3b1f-787e-82c3-6d897f549f6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_019dd587-3b1f-76c1-bf44-6ff20fd02a58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7b33-a5ce-84153963ef20" xlink:to="loc_us-gaap_IntersegmentEliminationMember_019dd587-3b1f-76c1-bf44-6ff20fd02a58" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-79a4-b98f-579436f56073" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-79a4-b98f-579436f56073" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-79a4-b98f-579436f56073_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-79a4-b98f-579436f56073" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-79a4-b98f-579436f56073_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7618-a81a-a5291fc9a1ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-79a4-b98f-579436f56073" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7618-a81a-a5291fc9a1ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3b1f-75ff-bcf4-d17659092b19" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-7618-a81a-a5291fc9a1ad" xlink:to="loc_dpl_UtilityMember_019dd587-3b1f-75ff-bcf4-d17659092b19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7932-99fd-b24d79a531da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7932-99fd-b24d79a531da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7932-99fd-b24d79a531da_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7932-99fd-b24d79a531da" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7932-99fd-b24d79a531da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7245-a0d5-92edf9fdf48f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7932-99fd-b24d79a531da" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7245-a0d5-92edf9fdf48f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7ae3-be8d-75c3181b12c8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7245-a0d5-92edf9fdf48f" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7ae3-be8d-75c3181b12c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-7ea7-88ea-facc59c50cf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-7ea7-88ea-facc59c50cf6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-7ea7-88ea-facc59c50cf6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-7ea7-88ea-facc59c50cf6" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-7ea7-88ea-facc59c50cf6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-72c2-87e9-aa775ae224ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-7ea7-88ea-facc59c50cf6" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-72c2-87e9-aa775ae224ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-3b1f-7d21-91bc-d6c9cbd7c4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-72c2-87e9-aa775ae224ae" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-3b1f-7d21-91bc-d6c9cbd7c4f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7fba-bb1e-7075fda63348" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-709f-85d2-e26cdb0aec5a" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7fba-bb1e-7075fda63348" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7fba-bb1e-7075fda63348_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7fba-bb1e-7075fda63348" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7fba-bb1e-7075fda63348_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7d8d-8098-8bfc1a1d7e78" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7fba-bb1e-7075fda63348" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7d8d-8098-8bfc1a1d7e78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueFromExternalCustomersMember_019dd587-3b1f-71f2-9caf-b78a19eeef91" xlink:href="dpl-20260331.xsd#dpl_RevenueFromExternalCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7d8d-8098-8bfc1a1d7e78" xlink:to="loc_dpl_RevenueFromExternalCustomersMember_019dd587-3b1f-71f2-9caf-b78a19eeef91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IntersegmentRevenueMember_019dd587-3b1f-78d3-a0d2-5ee54f3ba5c8" xlink:href="dpl-20260331.xsd#dpl_IntersegmentRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7d8d-8098-8bfc1a1d7e78" xlink:to="loc_dpl_IntersegmentRevenueMember_019dd587-3b1f-78d3-a0d2-5ee54f3ba5c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019dd587-3b1f-730a-b1e8-df7e21b1d411" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019dd587-3b1f-730a-b1e8-df7e21b1d411" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_019dd587-3b1f-789e-896c-ea1682ad63fc" xlink:href="dpl-20260331.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_dpl_NumberOfRetailCustomers_019dd587-3b1f-789e-896c-ea1682ad63fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_019dd587-3b1f-70df-bd30-ad089b29b2b7" xlink:href="dpl-20260331.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_dpl_ServiceAreaSquareMiles_019dd587-3b1f-70df-bd30-ad089b29b2b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-3b1f-7dd9-b9d0-55c5e505d6e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_us-gaap_Assets_019dd587-3b1f-7dd9-b9d0-55c5e505d6e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-3b1f-7b62-aa70-edd3eadcd17f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_us-gaap_Revenues_019dd587-3b1f-7b62-aa70-edd3eadcd17f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-3b1f-74c9-af9b-6ba2c0c4e410" xlink:href="dpl-20260331.xsd#dpl_ElectricRevenueIncludingDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-3b1f-74c9-af9b-6ba2c0c4e410" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019de444-efaf-7814-96b0-8bfaececd533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-764c-bb27-f8e1dda532d1" xlink:to="loc_us-gaap_NumberOfReportableSegments_019de444-efaf-7814-96b0-8bfaececd533" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsSegmentFinancialInformationDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsSegmentFinancialInformationDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsSegmentFinancialInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7cd1-a183-83c6db0b0e1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7cd1-a183-83c6db0b0e1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7cd1-a183-83c6db0b0e1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7cd1-a183-83c6db0b0e1c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7cd1-a183-83c6db0b0e1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7124-a0ad-4e8d6373c3c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7cd1-a183-83c6db0b0e1c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7124-a0ad-4e8d6373c3c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70c9-9470-80a0b473be63" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70c9-9470-80a0b473be63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70c9-9470-80a0b473be63_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70c9-9470-80a0b473be63" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-70c9-9470-80a0b473be63_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-747f-a647-680607e9457a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-70c9-9470-80a0b473be63" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-747f-a647-680607e9457a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7d01-99fd-863585b27f83" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-747f-a647-680607e9457a" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7d01-99fd-863585b27f83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-725f-9d0a-996c92c49817" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-725f-9d0a-996c92c49817" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-725f-9d0a-996c92c49817_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-725f-9d0a-996c92c49817" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-725f-9d0a-996c92c49817_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-3b1f-725f-9d0a-996c92c49817" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-742c-8d47-44126a2c2b44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-3b1f-742c-8d47-44126a2c2b44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019dd587-3b1f-735f-9e67-29857b2f9244" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019dd587-3b1f-735f-9e67-29857b2f9244" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_019dd587-3b1f-728a-b0c8-5fde611a09d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:to="loc_us-gaap_IntersegmentEliminationMember_019dd587-3b1f-728a-b0c8-5fde611a09d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_019dd587-3b1f-7aa2-80ed-cf509b3abdb8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-3b1f-7af1-bb87-5ae20d932634" xlink:to="loc_srt_ConsolidationEliminationsMember_019dd587-3b1f-7aa2-80ed-cf509b3abdb8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7470-a59c-e7ebf2892883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7470-a59c-e7ebf2892883" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7470-a59c-e7ebf2892883_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7470-a59c-e7ebf2892883" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7470-a59c-e7ebf2892883_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7a27-94a6-fce455355836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7470-a59c-e7ebf2892883" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7a27-94a6-fce455355836" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3b1f-7507-b37b-048ad02abbbe" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-7a27-94a6-fce455355836" xlink:to="loc_dpl_UtilityMember_019dd587-3b1f-7507-b37b-048ad02abbbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-72eb-86d6-7a7d985590e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-72eb-86d6-7a7d985590e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-72eb-86d6-7a7d985590e3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-72eb-86d6-7a7d985590e3" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-72eb-86d6-7a7d985590e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-7dd5-a5ff-c8264bcd746b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-3b1f-72eb-86d6-7a7d985590e3" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-7dd5-a5ff-c8264bcd746b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-3b1f-7bcf-8768-8671d21d44df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-3b1f-7dd5-a5ff-c8264bcd746b" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-3b1f-7bcf-8768-8671d21d44df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-3b1f-751a-9988-74f0ccc80f8b" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-3b1f-7b1e-a70a-91790670b872" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-3b1f-751a-9988-74f0ccc80f8b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-751a-9988-74f0ccc80f8b_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-751a-9988-74f0ccc80f8b" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-751a-9988-74f0ccc80f8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7ba6-bbd3-bde340c4df13" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-751a-9988-74f0ccc80f8b" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7ba6-bbd3-bde340c4df13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueFromExternalCustomersMember_019dd587-3b1f-71e0-a8ce-91f81782113a" xlink:href="dpl-20260331.xsd#dpl_RevenueFromExternalCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7ba6-bbd3-bde340c4df13" xlink:to="loc_dpl_RevenueFromExternalCustomersMember_019dd587-3b1f-71e0-a8ce-91f81782113a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IntersegmentRevenueMember_019dd587-3b1f-7550-812e-27770450c6b7" xlink:href="dpl-20260331.xsd#dpl_IntersegmentRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7ba6-bbd3-bde340c4df13" xlink:to="loc_dpl_IntersegmentRevenueMember_019dd587-3b1f-7550-812e-27770450c6b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ExternalCustomerRevenues_019dd587-3b1f-708a-8f31-2d01e6efcfae" xlink:href="dpl-20260331.xsd#dpl_ExternalCustomerRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_dpl_ExternalCustomerRevenues_019dd587-3b1f-708a-8f31-2d01e6efcfae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-3b1f-7226-bc38-787676d2f3d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_Revenues_019dd587-3b1f-7226-bc38-787676d2f3d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-3b1f-7b7d-9fb5-591c7ca1da10" xlink:href="dpl-20260331.xsd#dpl_ElectricRevenueIncludingDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-3b1f-7b7d-9fb5-591c7ca1da10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-3b1f-722a-ad23-e5095800ca8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-3b1f-722a-ad23-e5095800ca8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-3b1f-751d-84d9-827cffd6f953" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-3b1f-751d-84d9-827cffd6f953" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dd587-3b1f-7d4f-9f7e-0ad00ccfd972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dd587-3b1f-7d4f-9f7e-0ad00ccfd972" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-3b1f-7043-ae30-29120cade852" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_Assets_019dd587-3b1f-7043-ae30-29120cade852" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-3b1f-7d27-8a22-58184ef5bd4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpensePurchasedPower"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-3b1f-7d27-8a22-58184ef5bd4e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-3b1f-7704-a5e8-708666c8d243" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-3b1f-7704-a5e8-708666c8d243" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-3b1f-7a95-9183-0daf05a2cf83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-3b1f-7a95-9183-0daf05a2cf83" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_019dd587-3b1f-7083-9794-4bdb8298516f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_OtherExpenses_019dd587-3b1f-7083-9794-4bdb8298516f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-3b1f-74ec-a205-04657932027f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-3b1f-74ec-a205-04657932027f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-3b1f-7e59-bde0-6802ff7b9b80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-3b1f-7e59-bde0-6802ff7b9b80" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3b1f-7dd9-a5da-44039935eca9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-3b1f-7dd9-a5da-44039935eca9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-3b1f-7299-bbda-f4b245d598ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-3b1f-7299-bbda-f4b245d598ec" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-3b1f-7976-a45e-c2e2f01a90cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-3b1f-7976-a45e-c2e2f01a90cc" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-3b1f-711d-8889-865b38cd9f60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-3b1f-711d-8889-865b38cd9f60" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-3b1f-7214-a91e-803cbfc39aa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-3b1f-7214-a91e-803cbfc39aa1" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-3b1f-76a5-a03c-463aa0803641" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-3b1f-7bce-bdae-5a151ee18292" xlink:to="loc_us-gaap_ProfitLoss_019dd587-3b1f-76a5-a03c-463aa0803641" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019dd587-3b1f-7e23-a11a-98cf3784e5af" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:to="loc_srt_ProductOrServiceAxis_019dd587-3b1f-7e23-a11a-98cf3784e5af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-7e23-a11a-98cf3784e5af_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019dd587-3b1f-7e23-a11a-98cf3784e5af" xlink:to="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-7e23-a11a-98cf3784e5af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-753e-8cdb-0706130b9ae3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019dd587-3b1f-7e23-a11a-98cf3784e5af" xlink:to="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-753e-8cdb-0706130b9ae3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_019dd587-3b1f-721c-b425-3a93ee3c559a" xlink:href="dpl-20260331.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-753e-8cdb-0706130b9ae3" xlink:to="loc_dpl_OtherRevenuesMember_019dd587-3b1f-721c-b425-3a93ee3c559a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_WholesaleRevenueMember_019dd587-3b1f-79d0-8e16-0973d2410ee6" xlink:href="dpl-20260331.xsd#dpl_WholesaleRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-753e-8cdb-0706130b9ae3" xlink:to="loc_dpl_WholesaleRevenueMember_019dd587-3b1f-79d0-8e16-0973d2410ee6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RetailRevenueMember_019dd587-3b1f-7505-9c12-70cee4bf6cee" xlink:href="dpl-20260331.xsd#dpl_RetailRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-3b1f-753e-8cdb-0706130b9ae3" xlink:to="loc_dpl_RetailRevenueMember_019dd587-3b1f-7505-9c12-70cee4bf6cee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7319-8592-faabac24d750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7319-8592-faabac24d750" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-7319-8592-faabac24d750_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7319-8592-faabac24d750" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-7319-8592-faabac24d750_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-3b1f-76d8-b7d6-27f97041917c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-3b1f-7319-8592-faabac24d750" xlink:to="loc_us-gaap_SegmentDomain_019dd587-3b1f-76d8-b7d6-27f97041917c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-3b1f-7419-8210-4a728cf880bc" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-76d8-b7d6-27f97041917c" xlink:to="loc_dpl_UtilityMember_019dd587-3b1f-7419-8210-4a728cf880bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019dd587-3b1f-7c18-ba4d-545d657dbafb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-76d8-b7d6-27f97041917c" xlink:to="loc_us-gaap_CorporateAndOtherMember_019dd587-3b1f-7c18-ba4d-545d657dbafb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AdjustmentsAndEliminationsMember_019dd587-3b1f-7b23-96a9-af62dd041fba" xlink:href="dpl-20260331.xsd#dpl_AdjustmentsAndEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-3b1f-76d8-b7d6-27f97041917c" xlink:to="loc_dpl_AdjustmentsAndEliminationsMember_019dd587-3b1f-7b23-96a9-af62dd041fba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7919-aa42-d8d31249a8cd" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7919-aa42-d8d31249a8cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7919-aa42-d8d31249a8cd_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7919-aa42-d8d31249a8cd" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7919-aa42-d8d31249a8cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-3b1f-7919-aa42-d8d31249a8cd" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ResidentialRevenueMember_019dd587-3b1f-787f-b551-6aa4079f996f" xlink:href="dpl-20260331.xsd#dpl_ResidentialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:to="loc_dpl_ResidentialRevenueMember_019dd587-3b1f-787f-b551-6aa4079f996f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CommercialRevenueMember_019dd587-3b1f-7a4d-8aa2-1b2b9aefa85c" xlink:href="dpl-20260331.xsd#dpl_CommercialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:to="loc_dpl_CommercialRevenueMember_019dd587-3b1f-7a4d-8aa2-1b2b9aefa85c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IndustrialRevenueMember_019dd587-3b1f-76bd-8e2a-e8fa4ebf6cf7" xlink:href="dpl-20260331.xsd#dpl_IndustrialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:to="loc_dpl_IndustrialRevenueMember_019dd587-3b1f-76bd-8e2a-e8fa4ebf6cf7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_GovernmentalRevenueMember_019dd587-3b1f-7c6c-9108-34c96ba9eae3" xlink:href="dpl-20260331.xsd#dpl_GovernmentalRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:to="loc_dpl_GovernmentalRevenueMember_019dd587-3b1f-7c6c-9108-34c96ba9eae3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_019dd587-3b1f-7777-a00e-6abce7e993db" xlink:href="dpl-20260331.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-3b1f-7322-86ff-07fd897e5680" xlink:to="loc_dpl_OtherRevenuesMember_019dd587-3b1f-7777-a00e-6abce7e993db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-77e2-a109-48eca85f2bd7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-72d8-9af7-829d21e74aee" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-77e2-a109-48eca85f2bd7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77e2-a109-48eca85f2bd7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-77e2-a109-48eca85f2bd7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-77e2-a109-48eca85f2bd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-a496-1ab7c228e983" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-77e2-a109-48eca85f2bd7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-a496-1ab7c228e983" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-79bf-aae5-405bfbfcf08f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7ace-a496-1ab7c228e983" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-79bf-aae5-405bfbfcf08f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019dd587-3b1f-7aeb-ad5f-e6f8c51b48e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019dd587-3b1f-7aeb-ad5f-e6f8c51b48e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Othernon606revenue_019dd587-3b1f-7f1c-b2b5-34f6a701fc3d" xlink:href="dpl-20260331.xsd#dpl_Othernon606revenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_dpl_Othernon606revenue_019dd587-3b1f-7f1c-b2b5-34f6a701fc3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTORevenue_019dd587-3b1f-7b81-920a-d5f860432b8a" xlink:href="dpl-20260331.xsd#dpl_RTORevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_dpl_RTORevenue_019dd587-3b1f-7b81-920a-d5f860432b8a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTOCapacityRevenue_019dd587-3b1f-710a-ae0c-4be21bd5683a" xlink:href="dpl-20260331.xsd#dpl_RTOCapacityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_dpl_RTOCapacityRevenue_019dd587-3b1f-710a-ae0c-4be21bd5683a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-3b1f-74ba-b056-f52e94dd4910" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_us-gaap_Revenues_019dd587-3b1f-74ba-b056-f52e94dd4910" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-3b1f-7688-a08f-fe1947c4d0d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7afc-8a31-b25d6a24bcd0" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-3b1f-7688-a08f-fe1947c4d0d2" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FixedassetImpairmentFixedassetImpairmentDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FixedassetImpairmentFixedassetImpairmentDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FixedassetImpairmentFixedassetImpairmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-3b1f-7807-aefc-ae3eb8ffe0bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-3b1f-7d36-8c6d-6549e4dc92c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-3b1f-7807-aefc-ae3eb8ffe0bb" xlink:to="loc_us-gaap_StatementTable_019dd587-3b1f-7d36-8c6d-6549e4dc92c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-78a0-99a7-77e07060c974" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7d36-8c6d-6549e4dc92c5" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-78a0-99a7-77e07060c974" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-78a0-99a7-77e07060c974_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-78a0-99a7-77e07060c974" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-78a0-99a7-77e07060c974_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-795e-b1b1-c4a255f399be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-3b1f-78a0-99a7-77e07060c974" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-795e-b1b1-c4a255f399be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-78c4-b576-3d3f9001d00c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-3b1f-795e-b1b1-c4a255f399be" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-3b1f-78c4-b576-3d3f9001d00c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7378-a25e-ae7dd82a23bd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-3b1f-7d36-8c6d-6549e4dc92c5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7378-a25e-ae7dd82a23bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7378-a25e-ae7dd82a23bd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7378-a25e-ae7dd82a23bd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7378-a25e-ae7dd82a23bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e4b-8957-0dd8d746522e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7378-a25e-ae7dd82a23bd" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e4b-8957-0dd8d746522e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7ee9-ac02-75a809d0a9bb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7e4b-8957-0dd8d746522e" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7ee9-ac02-75a809d0a9bb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7aac-b7eb-332cbd4c405a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7aac-b7eb-332cbd4c405a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ConesvilleMember_019dd587-3b1f-7a68-b970-a4d09ec3bf33" xlink:href="dpl-20260331.xsd#dpl_ConesvilleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:to="loc_dpl_ConesvilleMember_019dd587-3b1f-7a68-b970-a4d09ec3bf33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72a8-93df-8c25d4a55424_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72a8-93df-8c25d4a55424_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-702a-9e1e-c994d5239ce7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-702a-9e1e-c994d5239ce7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7588-9d15-9dedd7101efd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7588-9d15-9dedd7101efd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7108-a533-0d21f17054f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7108-a533-0d21f17054f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7677-92ec-a732ca82f6dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7677-92ec-a732ca82f6dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7532-8b2f-fd8f483e2266" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7532-8b2f-fd8f483e2266" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-75bd-a44d-87751139a222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-3b1f-75bd-a44d-87751139a222" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7e83-8285-9f827ddc85cb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7e83-8285-9f827ddc85cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7369-9676-e2f1c718dbe0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7369-9676-e2f1c718dbe0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3b1f-71d5-8020-ae0ae259060f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3b1f-71d5-8020-ae0ae259060f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-3b1f-7c0c-ab39-f665577deaf2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-3b1f-7c0c-ab39-f665577deaf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-3b1f-77c0-a499-a0539ce5e372" xlink:href="dpl-20260331.xsd#dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-3b1f-77c0-a499-a0539ce5e372" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-3b1f-7ae2-a0fb-b38115443d47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-3b1f-7ae2-a0fb-b38115443d47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-3b1f-7305-b0d9-86dd6a5274bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-3b1f-7305-b0d9-86dd6a5274bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-72c4-b45c-ce9e8d1af172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-72c4-b45c-ce9e8d1af172" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-794c-8b79-20753dab44cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7aa1-9225-22ee2e149406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7aa1-9225-22ee2e149406" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7e66-9a9d-ffe7881d1f01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsDetails_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsDetails_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7aac-b7eb-332cbd4c405a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7aac-b7eb-332cbd4c405a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-3b1f-7aac-b7eb-332cbd4c405a" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ConesvilleMember_019dd587-3b1f-7a68-b970-a4d09ec3bf33" xlink:href="dpl-20260331.xsd#dpl_ConesvilleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-3b1f-7732-92d7-c6d97de833ff" xlink:to="loc_dpl_ConesvilleMember_019dd587-3b1f-7a68-b970-a4d09ec3bf33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72a8-93df-8c25d4a55424_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-72a8-93df-8c25d4a55424_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-72a8-93df-8c25d4a55424" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-702a-9e1e-c994d5239ce7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-798c-8b8a-58e92492aa44" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-702a-9e1e-c994d5239ce7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7588-9d15-9dedd7101efd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7588-9d15-9dedd7101efd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7108-a533-0d21f17054f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-3b1f-7588-9d15-9dedd7101efd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-3b1f-7108-a533-0d21f17054f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7677-92ec-a732ca82f6dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7677-92ec-a732ca82f6dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7532-8b2f-fd8f483e2266" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-3b1f-7677-92ec-a732ca82f6dd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-3b1f-7532-8b2f-fd8f483e2266" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-3b1f-77fd-bd4f-8a6e8dbe864a" xlink:to="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7e83-8285-9f827ddc85cb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7e83-8285-9f827ddc85cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-3b1f-7e83-8285-9f827ddc85cb" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-3b1f-7369-9676-e2f1c718dbe0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-3b1f-7edd-9ecf-f9e9f16aea2b" xlink:to="loc_srt_ScenarioForecastMember_019dd587-3b1f-7369-9676-e2f1c718dbe0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3b1f-71d5-8020-ae0ae259060f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-3b1f-71d5-8020-ae0ae259060f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-3b1f-7c0c-ab39-f665577deaf2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-3b1f-7c0c-ab39-f665577deaf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-3b1f-77c0-a499-a0539ce5e372" xlink:href="dpl-20260331.xsd#dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-3b1f-77c0-a499-a0539ce5e372" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-3b1f-7ae2-a0fb-b38115443d47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-3b1f-7ae2-a0fb-b38115443d47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-3b1f-7305-b0d9-86dd6a5274bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-3b1f-7305-b0d9-86dd6a5274bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-72c4-b45c-ce9e8d1af172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-72c4-b45c-ce9e8d1af172" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-3b1f-794c-8b79-20753dab44cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7aa1-9225-22ee2e149406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-3b1f-7db2-9598-39375017c88b" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7aa1-9225-22ee2e149406" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-3b1f-7e66-9a9d-ffe7881d1f01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RiskUncertaintiesDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RiskUncertaintiesDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RiskUncertaintiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-3b1f-7e77-88c4-49a9f108d4a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-78b9-8b55-b8b0315cf960" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-3b1f-7e77-88c4-49a9f108d4a7" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-78b9-8b55-b8b0315cf960" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fe1-9ea5-8f16bd202c59" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-3b1f-78b9-8b55-b8b0315cf960" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fe1-9ea5-8f16bd202c59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fe1-9ea5-8f16bd202c59_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fe1-9ea5-8f16bd202c59" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7fe1-9ea5-8f16bd202c59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7cb6-b965-d60bc1d24b6c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-3b1f-7fe1-9ea5-8f16bd202c59" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7cb6-b965-d60bc1d24b6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-3b1f-7dd9-a329-442d89cdbaa5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-3b1f-7cb6-b965-d60bc1d24b6c" xlink:to="loc_srt_SubsidiariesMember_019dd587-3b1f-7dd9-a329-442d89cdbaa5" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
