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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a063ef-fdd0-7194-b463-468d2a3fe542,g:557aad68-1b03-49b0-bb69-d61cb37a9888-->
<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-20260930.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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-fe70-7c4f-a1af-6b8c684b1faa" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntitiesTable_01a063ef-fe70-7c4f-a1af-6b8c684b1faa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-fe70-7ed7-989a-862742bdb7d8" 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_01a063ef-fe70-7c4f-a1af-6b8c684b1faa" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-fe70-7ed7-989a-862742bdb7d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7ed7-989a-862742bdb7d8_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_01a063ef-fe70-7ed7-989a-862742bdb7d8" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7ed7-989a-862742bdb7d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7c32-86da-6438524be75d" 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_01a063ef-fe70-7ed7-989a-862742bdb7d8" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7c32-86da-6438524be75d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-fe70-71fa-bc31-05ab96dc004e" 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_01a063ef-fe70-7c32-86da-6438524be75d" xlink:to="loc_srt_SubsidiariesMember_01a063ef-fe70-71fa-bc31-05ab96dc004e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_01a063ef-fe70-7e23-a647-795794ef67a7" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentFiscalYearFocus_01a063ef-fe70-7e23-a647-795794ef67a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_01a063ef-fe70-7cff-85c1-895808338a48" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentFiscalPeriodFocus_01a063ef-fe70-7cff-85c1-895808338a48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a063ef-fe70-7565-872f-5fc258650e86" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityCentralIndexKey_01a063ef-fe70-7565-872f-5fc258650e86" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_01a063ef-fe70-7e48-acd9-eecc26f7113b" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_CurrentFiscalYearEndDate_01a063ef-fe70-7e48-acd9-eecc26f7113b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a063ef-fe70-778d-92d6-541c5aea21a9" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_AmendmentFlag_01a063ef-fe70-778d-92d6-541c5aea21a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_01a063ef-fe70-7e52-b946-6e1edeae1e54" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityCurrentReportingStatus_01a063ef-fe70-7e52-b946-6e1edeae1e54" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_01a063ef-fe70-7701-a20d-17f95148cc52" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentType_01a063ef-fe70-7701-a20d-17f95148cc52" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_01a063ef-fe70-7e2d-9b20-27044e97ec0c" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentQuarterlyReport_01a063ef-fe70-7e2d-9b20-27044e97ec0c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_01a063ef-fe70-7157-8742-5f48cb48c205" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityInteractiveDataCurrent_01a063ef-fe70-7157-8742-5f48cb48c205" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_01a063ef-fe70-7f5d-a241-c394d2316cf0" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityFilerCategory_01a063ef-fe70-7f5d-a241-c394d2316cf0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_01a063ef-fe70-702e-8e90-5fea7fcf912b" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityShellCompany_01a063ef-fe70-702e-8e90-5fea7fcf912b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_01a063ef-fe70-7007-ae9c-ad50850584fc" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentPeriodEndDate_01a063ef-fe70-7007-ae9c-ad50850584fc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_01a063ef-fe70-7c6e-ab53-65a72bf680eb" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_DocumentTransitionReport_01a063ef-fe70-7c6e-ab53-65a72bf680eb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_01a063ef-fe70-7cb9-a243-7a33abdda985" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityRegistrantName_01a063ef-fe70-7cb9-a243-7a33abdda985" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a063ef-fe70-7b33-bd8a-9050ce784055" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a063ef-fe70-7b33-bd8a-9050ce784055" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a063ef-fe70-7e9f-aaec-461201390006" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityFileNumber_01a063ef-fe70-7e9f-aaec-461201390006" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_01a063ef-fe70-701a-aaef-817ed379e580" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityAddressAddressLine1_01a063ef-fe70-701a-aaef-817ed379e580" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_01a063ef-fe70-78b5-8c44-c98f0fbf6e84" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityAddressPostalZipCode_01a063ef-fe70-78b5-8c44-c98f0fbf6e84" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_01a063ef-fe70-784d-95be-f10b11fa58ab" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_LocalPhoneNumber_01a063ef-fe70-784d-95be-f10b11fa58ab" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a063ef-fe70-7375-b73e-6fb04a688ca9" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a063ef-fe70-7375-b73e-6fb04a688ca9" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_01a063ef-fe70-7514-892a-b06d51f0a9fb" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntitySmallBusiness_01a063ef-fe70-7514-892a-b06d51f0a9fb" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a063ef-fe70-7e01-8344-16e46f2b5dc8" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a063ef-fe70-7e01-8344-16e46f2b5dc8" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_01a063ef-fe70-7358-b76c-91b4fa80983e" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_01a063ef-fe70-7358-b76c-91b4fa80983e" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_01a063ef-fe70-7372-97f2-c58fc55d4f68" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityAddressCityOrTown_01a063ef-fe70-7372-97f2-c58fc55d4f68" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_01a063ef-fe70-73b6-a160-c99fd678f97b" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_EntityAddressStateOrProvince_01a063ef-fe70-73b6-a160-c99fd678f97b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_01a063ef-fe70-7eda-baee-b1a837d73139" 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_01a063ef-fe70-7194-b1d3-6c8d3c44e043" xlink:to="loc_dei_CityAreaCode_01a063ef-fe70-7eda-baee-b1a837d73139" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7fe1-b539-8f1674ade925" 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_01a063ef-fe70-7910-9a38-835b4e15cc8f" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-7910-9a38-835b4e15cc8f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a063ef-fe70-7995-af1b-9a56a1e3f60b" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_Revenues_01a063ef-fe70-7995-af1b-9a56a1e3f60b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-fe70-7867-8900-5f78a146a9bf" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-fe70-7867-8900-5f78a146a9bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-fe70-7a1f-aea5-7af782e71b47" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-fe70-7a1f-aea5-7af782e71b47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a063ef-fe70-7d66-94fa-8dd5f1515c27" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_CostsAndExpenses_01a063ef-fe70-7d66-94fa-8dd5f1515c27" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a063ef-fe70-70b1-8f3c-2465de4500f0" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a063ef-fe70-70b1-8f3c-2465de4500f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_01a063ef-fe70-773b-b85d-17fdf385974d" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_InterestAndDebtExpense_01a063ef-fe70-773b-b85d-17fdf385974d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-fe70-7d98-9e5d-bac9abda11c6" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-fe70-7d98-9e5d-bac9abda11c6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-705b-96b5-89561d50fd6f" 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_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-705b-96b5-89561d50fd6f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-fe70-74cc-ab2c-cd729b61ca1e" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-fe70-74cc-ab2c-cd729b61ca1e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-fe70-72f9-a83a-4f1f261475b2" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-fe70-72f9-a83a-4f1f261475b2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_01a063ef-fe70-7bdc-a48a-d3f081603ba1" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_01a063ef-fe70-7bdc-a48a-d3f081603ba1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_01a063ef-fe70-7c5c-8123-4cc515090839" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_01a063ef-fe70-7c5c-8123-4cc515090839" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-fe70-7cb4-95a3-47a638814f3f" 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_StatementLineItems_01a063ef-fe70-7fe1-b539-8f1674ade925" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-fe70-7cb4-95a3-47a638814f3f" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-77d6-a25a-96fbf404a998" 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_01a063ef-fe70-783d-8576-ea0d5211a1e2" 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_01a063ef-fe70-77d6-a25a-96fbf404a998" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-783d-8576-ea0d5211a1e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2" 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_01a063ef-fe70-783d-8576-ea0d5211a1e2" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2_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_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7d45-b9e7-f0614690d751" 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_01a063ef-fe70-7ea3-8920-7cd1ee7a44d2" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7d45-b9e7-f0614690d751" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a063ef-fe70-78e1-8d45-a717564f2fdc" 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_01a063ef-fe70-7d45-b9e7-f0614690d751" xlink:to="loc_us-gaap_RetainedEarningsMember_01a063ef-fe70-78e1-8d45-a717564f2fdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-7beb-90c9-467aa3aa1331" 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_01a063ef-fe70-77d6-a25a-96fbf404a998" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-7beb-90c9-467aa3aa1331" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_01a063ef-fe70-74cb-9bc3-d0bdab69340b" 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_01a063ef-fe70-77d6-a25a-96fbf404a998" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_01a063ef-fe70-74cb-9bc3-d0bdab69340b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_01a063ef-fe70-7589-8868-5aa61784f358" 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_01a063ef-fe70-77d6-a25a-96fbf404a998" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_01a063ef-fe70-7589-8868-5aa61784f358" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-fe70-74e6-bcde-2055e2938b24" 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_01a063ef-fe70-7589-8868-5aa61784f358" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-fe70-74e6-bcde-2055e2938b24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7d8c-a936-3015497e32b0" 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_01a063ef-fe70-7589-8868-5aa61784f358" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7d8c-a936-3015497e32b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_01a063ef-fe70-799a-851e-6fefe9a562f0" 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_01a063ef-fe70-77d6-a25a-96fbf404a998" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_01a063ef-fe70-799a-851e-6fefe9a562f0" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7ed9-a51e-3244f77a3814" 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_01a063ef-fe70-776b-a4e3-ba05ba2aa64e" 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_01a063ef-fe70-7ed9-a51e-3244f77a3814" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-776b-a4e3-ba05ba2aa64e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_01a063ef-fe70-7d34-9555-ae8136093da5" 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_01a063ef-fe70-7ed9-a51e-3244f77a3814" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_01a063ef-fe70-7d34-9555-ae8136093da5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" 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_01a063ef-fe70-7dd3-bd85-9af54a607b80" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-7dd3-bd85-9af54a607b80" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a063ef-fe70-739f-9182-64e9e26ceb85" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" 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_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_01a063ef-fe70-7b84-82b1-e8f85f53f023" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_DebtCurrent_01a063ef-fe70-7b84-82b1-e8f85f53f023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_01a063ef-fe70-7d33-a412-8278e83ba0de" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_AccountsPayableCurrent_01a063ef-fe70-7d33-a412-8278e83ba0de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_01a063ef-fe70-7ef0-854c-016d598bdffe" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_TaxesPayableCurrent_01a063ef-fe70-7ef0-854c-016d598bdffe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_01a063ef-fe70-71a3-b643-b343371d9505" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_InterestPayableCurrent_01a063ef-fe70-71a3-b643-b343371d9505" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a063ef-fe70-7684-bb31-4697198bcc1f" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a063ef-fe70-7684-bb31-4697198bcc1f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_01a063ef-fe70-7a5e-aef8-afebb91102cd" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_01a063ef-fe70-7a5e-aef8-afebb91102cd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_01a063ef-fe70-73d8-80cf-9e4f4a7c240d" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_01a063ef-fe70-73d8-80cf-9e4f4a7c240d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_01a063ef-fe70-77b4-9f45-cc0d7716e4a1" 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_01a063ef-fe70-74a7-ba91-53f00a9e5cc9" xlink:to="loc_us-gaap_LiabilitiesCurrent_01a063ef-fe70-77b4-9f45-cc0d7716e4a1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" 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_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-fe70-740a-895b-e2387f72a86f" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-fe70-740a-895b-e2387f72a86f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_01a063ef-fe70-7a99-a144-2eb079540884" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_01a063ef-fe70-7a99-a144-2eb079540884" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a063ef-fe70-7fff-a3a4-e915d63949ab" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a063ef-fe70-7fff-a3a4-e915d63949ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_01a063ef-fe70-7dbb-93da-0da97ce68cc0" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_01a063ef-fe70-7dbb-93da-0da97ce68cc0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_01a063ef-fe70-7854-81b4-3887eed18f23" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_01a063ef-fe70-7854-81b4-3887eed18f23" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_01a063ef-fe70-7c84-8018-5934bbfe736a" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_01a063ef-fe70-7c84-8018-5934bbfe736a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_01a063ef-fe70-70f7-8c69-46c966c20a05" 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_01a063ef-fe70-7c3b-bd0c-f6b775f9e257" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_01a063ef-fe70-70f7-8c69-46c966c20a05" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-78e2-be4e-98e6fbd10e04" 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_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-78e2-be4e-98e6fbd10e04" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_01a063ef-fe70-7719-9c3b-4f9d43ef1c69" 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_LiabilitiesAndStockholdersEquityAbstract_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_SharesIssued_01a063ef-fe70-7719-9c3b-4f9d43ef1c69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_01a063ef-fe70-748b-af36-f2f060d9facd" 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_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_01a063ef-fe70-790d-8a03-0e266811aaef" 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_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:to="loc_us-gaap_CommonStockValue_01a063ef-fe70-790d-8a03-0e266811aaef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_01a063ef-fe70-70a6-98b6-da1d2d569b92" 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_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_01a063ef-fe70-70a6-98b6-da1d2d569b92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7c1a-8ecb-cc4a4357f463" 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_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7c1a-8ecb-cc4a4357f463" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a063ef-fe70-722f-95f0-781e6eb6b937" 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_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a063ef-fe70-722f-95f0-781e6eb6b937" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a063ef-fe70-7f68-9c2b-8c25e4352f7f" 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_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_01a063ef-fe70-748b-af36-f2f060d9facd" xlink:to="loc_us-gaap_StockholdersEquity_01a063ef-fe70-7f68-9c2b-8c25e4352f7f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a063ef-fe70-7999-993a-059472c88d93" 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_01a063ef-fe70-739f-9182-64e9e26ceb85" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a063ef-fe70-7999-993a-059472c88d93" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7bac-b2ba-525e076c84b6" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7bac-b2ba-525e076c84b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-744d-b5d3-7c569ea5cfcc" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-744d-b5d3-7c569ea5cfcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a063ef-fe70-7b16-85cf-dbaf44a44d0f" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_CommonStockSharesIssued_01a063ef-fe70-7b16-85cf-dbaf44a44d0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_01a063ef-fe70-7142-95e6-8f8cdd8cbfc6" 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_StatementLineItems_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_AssetsCurrent_01a063ef-fe70-7142-95e6-8f8cdd8cbfc6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-74de-b135-a1437c698e46" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-74de-b135-a1437c698e46" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-71ff-a3d0-141dbe56c3a4" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-71ff-a3d0-141dbe56c3a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_01a063ef-fe70-7ff6-b216-1a4b3394a3a9" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_InventoryNet_01a063ef-fe70-7ff6-b216-1a4b3394a3a9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_01a063ef-fe70-7ec3-89d5-f3910f34102e" xlink:href="dpl-20260930.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_01a063ef-fe70-7ec3-89d5-f3910f34102e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_01a063ef-fe70-75d5-8c27-cdfa889e1eb4" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_01a063ef-fe70-75d5-8c27-cdfa889e1eb4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_01a063ef-fe70-74ab-b9e1-71b792c1eca0" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_IncomeTaxesReceivable_01a063ef-fe70-74ab-b9e1-71b792c1eca0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_01a063ef-fe70-72ea-b382-ece6af16d504" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_OtherAssetsCurrent_01a063ef-fe70-72ea-b382-ece6af16d504" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a063ef-fe70-7c0e-a0cf-04129ebee0a6" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_Liabilities_01a063ef-fe70-7c0e-a0cf-04129ebee0a6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_01a063ef-fe70-738c-bdb7-81da0df2300d" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_01a063ef-fe70-738c-bdb7-81da0df2300d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7a77-9f89-c7ad88665953" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7a77-9f89-c7ad88665953" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a063ef-fe70-728e-95ce-53487013709e" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a063ef-fe70-728e-95ce-53487013709e" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a063ef-fe70-7da2-bb32-d18e63fd6210" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a063ef-fe70-7da2-bb32-d18e63fd6210" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_01a063ef-fe70-7e4d-8ee2-b7af808a8b84" 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_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_AssetsNoncurrent_01a063ef-fe70-7e4d-8ee2-b7af808a8b84" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a063ef-fe70-7543-b88a-f7cdd7a4b487" 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_StatementLineItems_01a063ef-fe70-747d-a2bb-b85fc6ca857b" xlink:to="loc_us-gaap_Assets_01a063ef-fe70-7543-b88a-f7cdd7a4b487" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7da1-83da-248a4b876d76" 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_01a063ef-fe70-7b29-9cc1-f8608540d95e" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-7b29-9cc1-f8608540d95e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-7c97-afda-eaaec4b8d90f" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-7c97-afda-eaaec4b8d90f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a063ef-fe70-7fc4-84cd-12f4a67d3146" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CommonStockSharesIssued_01a063ef-fe70-7fc4-84cd-12f4a67d3146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7a3f-8c27-4cd73e9b6026" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7a3f-8c27-4cd73e9b6026" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-723e-a9a2-5356a7db2c21" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-723e-a9a2-5356a7db2c21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a063ef-fe70-76f9-838c-aff7b45e4b70" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a063ef-fe70-76f9-838c-aff7b45e4b70" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-725a-8191-7e26db85b3cf" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-725a-8191-7e26db85b3cf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_01a063ef-fe70-7e67-ae82-5ab85cdaa749" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_01a063ef-fe70-7e67-ae82-5ab85cdaa749" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-7d59-9aad-4b5c560d544a" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-7d59-9aad-4b5c560d544a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_01a063ef-fe70-7935-b962-275a30c37f93" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_InventoryNet_01a063ef-fe70-7935-b962-275a30c37f93" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_01a063ef-fe70-7785-a007-8847fb359b63" xlink:href="dpl-20260930.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_01a063ef-fe70-7785-a007-8847fb359b63" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_01a063ef-fe70-75a6-866c-275d875c4e1d" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_01a063ef-fe70-75a6-866c-275d875c4e1d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_01a063ef-fe70-7c19-9849-63cc88d8f965" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_IncomeTaxesReceivable_01a063ef-fe70-7c19-9849-63cc88d8f965" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_01a063ef-fe70-7fb0-a33e-571a93ba086e" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_OtherAssetsCurrent_01a063ef-fe70-7fb0-a33e-571a93ba086e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a063ef-fe70-7946-827a-6f4a32957023" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a063ef-fe70-7946-827a-6f4a32957023" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7efc-b54c-3e66f8467e6b" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7efc-b54c-3e66f8467e6b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a063ef-fe70-7721-b688-c0cb93088f97" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a063ef-fe70-7721-b688-c0cb93088f97" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a063ef-fe70-7806-bf5e-dd00cc5bc01a" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a063ef-fe70-7806-bf5e-dd00cc5bc01a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_01a063ef-fe70-7248-9159-5e222d4155a2" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_LiabilitiesCurrent_01a063ef-fe70-7248-9159-5e222d4155a2" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_01a063ef-fe70-75c3-b49f-e5c7635b06f3" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_DebtCurrent_01a063ef-fe70-75c3-b49f-e5c7635b06f3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_01a063ef-fe70-77f5-9c6e-3104eecc4f60" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AccountsPayableCurrent_01a063ef-fe70-77f5-9c6e-3104eecc4f60" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_01a063ef-fe70-7695-9308-08a0c7d7722b" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_TaxesPayableCurrent_01a063ef-fe70-7695-9308-08a0c7d7722b" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_01a063ef-fe70-75b3-a500-f792f68bf62c" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_InterestPayableCurrent_01a063ef-fe70-75b3-a500-f792f68bf62c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a063ef-fe70-7cfd-8d93-f8993aae3797" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_01a063ef-fe70-7cfd-8d93-f8993aae3797" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_01a063ef-fe70-7468-ad95-d13360ef9d29" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_01a063ef-fe70-7468-ad95-d13360ef9d29" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_01a063ef-fe70-7740-9c8c-e3d992b10ee6" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_01a063ef-fe70-7740-9c8c-e3d992b10ee6" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-fe70-704b-9e5a-b09cb7943407" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-fe70-704b-9e5a-b09cb7943407" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_01a063ef-fe70-73c2-8dcc-8a47485a0513" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_01a063ef-fe70-73c2-8dcc-8a47485a0513" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a063ef-fe70-78c0-b648-af93150c2152" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_01a063ef-fe70-78c0-b648-af93150c2152" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_01a063ef-fe70-7277-9f9f-dccbfc9e92c4" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_01a063ef-fe70-7277-9f9f-dccbfc9e92c4" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_01a063ef-fe70-7e41-afdd-616e52e6f7eb" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_01a063ef-fe70-7e41-afdd-616e52e6f7eb" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_01a063ef-fe70-7977-be6a-a669b562bb75" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_01a063ef-fe70-7977-be6a-a669b562bb75" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_01a063ef-fe70-737f-8d21-5756aa91bfd5" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_CommonStockValue_01a063ef-fe70-737f-8d21-5756aa91bfd5" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_01a063ef-fe70-734e-a6df-c6700f05a094" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_01a063ef-fe70-734e-a6df-c6700f05a094" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7f2b-a507-2d37ef897724" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7f2b-a507-2d37ef897724" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a063ef-fe70-72f0-9d7f-01408a5deb5e" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a063ef-fe70-72f0-9d7f-01408a5deb5e" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a063ef-fe70-72a8-8971-bf3f0c7ef076" 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_01a063ef-fe70-7da1-83da-248a4b876d76" xlink:to="loc_us-gaap_Liabilities_01a063ef-fe70-72a8-8971-bf3f0c7ef076" xlink:type="arc" order="35"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" 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_01a063ef-fe70-75f8-a03d-80bb6e589932" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-75f8-a03d-80bb6e589932" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-7edb-8a3c-b5e7c6df809c" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-7edb-8a3c-b5e7c6df809c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-7223-8ce1-1eeead37252a" 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_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-7edb-8a3c-b5e7c6df809c" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-7223-8ce1-1eeead37252a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-78ed-a018-9158b7bd6b7a" 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_01a063ef-fe70-7edb-8a3c-b5e7c6df809c" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_01a063ef-fe70-7cb2-9bfa-e7c937a29376" xlink:href="dpl-20260930.xsd#dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:to="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_01a063ef-fe70-7cb2-9bfa-e7c937a29376" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_01a063ef-fe70-752f-97f1-474da54bafad" 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_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_01a063ef-fe70-752f-97f1-474da54bafad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_01a063ef-fe70-76a0-8c2c-c35957db4c39" 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_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_01a063ef-fe70-76a0-8c2c-c35957db4c39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInReceivables_01a063ef-fe70-74a2-b612-98e558e84cff" 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_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:to="loc_us-gaap_IncreaseDecreaseInReceivables_01a063ef-fe70-74a2-b612-98e558e84cff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a063ef-fe70-73b0-b5d0-fb4ad601d182" 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_01a063ef-fe70-78ed-a018-9158b7bd6b7a" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_01a063ef-fe70-78a7-9941-8b424b83f40a" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_01a063ef-fe70-78a7-9941-8b424b83f40a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_01a063ef-fe70-71e3-bb28-9aee7acb4631" xlink:href="dpl-20260930.xsd#dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_01a063ef-fe70-71e3-bb28-9aee7acb4631" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_01a063ef-fe70-7347-8bac-9d0e3de6c82e" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_01a063ef-fe70-7347-8bac-9d0e3de6c82e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_01a063ef-fe70-78e7-a931-f025a97ec375" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_01a063ef-fe70-78e7-a931-f025a97ec375" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_01a063ef-fe70-79a6-ace6-e01155dff2da" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_01a063ef-fe70-79a6-ace6-e01155dff2da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_01a063ef-fe70-7a93-b6b1-a8889ee2785b" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_01a063ef-fe70-7a93-b6b1-a8889ee2785b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_01a063ef-fe70-7cfd-86ca-f932cc23caf2" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_01a063ef-fe70-7cfd-86ca-f932cc23caf2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_01a063ef-fe70-7af4-bce8-286c21fe2af2" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_01a063ef-fe70-7af4-bce8-286c21fe2af2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_01a063ef-fe70-7a13-9228-1fd996fd77e7" 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_01a063ef-fe70-73b0-b5d0-fb4ad601d182" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_01a063ef-fe70-7a13-9228-1fd996fd77e7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a063ef-fe70-732d-bf02-5da03d1ee2c9" 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_01a063ef-fe70-7edb-8a3c-b5e7c6df809c" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a063ef-fe70-732d-bf02-5da03d1ee2c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a063ef-fe70-76ce-af2c-05cf5849668f" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_01a063ef-fe70-7e73-b8e1-5a61b67670e9" 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_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:to="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_01a063ef-fe70-7e73-b8e1-5a61b67670e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_01a063ef-fe70-7994-af43-1e928e4bdd3c" 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_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_01a063ef-fe70-7994-af43-1e928e4bdd3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_01a063ef-fe70-73ed-a04f-da2aaa17deda" 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_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_01a063ef-fe70-73ed-a04f-da2aaa17deda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_01a063ef-fe70-7b19-ab0c-500baf350965" 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_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_01a063ef-fe70-7b19-ab0c-500baf350965" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a063ef-fe70-70a4-8ce2-e215417da9fd" 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_01a063ef-fe70-76ce-af2c-05cf5849668f" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a063ef-fe70-70a4-8ce2-e215417da9fd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a063ef-fe70-7f10-8f33-829a7b0fa816" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_01a063ef-fe70-79f8-a1f8-38a103aaca1b" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_PaymentsOfDividends_01a063ef-fe70-79f8-a1f8-38a103aaca1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PaymentsOfDeferredFinanceCosts_01a063ef-fe70-788c-91ec-efa03a596a1b" xlink:href="dpl-20260930.xsd#dpl_PaymentsOfDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_dpl_PaymentsOfDeferredFinanceCosts_01a063ef-fe70-788c-91ec-efa03a596a1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_01a063ef-fe70-71d7-b48a-11faf632a437" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_01a063ef-fe70-71d7-b48a-11faf632a437" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_01a063ef-fe70-74ee-a4e3-36643a25b4bb" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_01a063ef-fe70-74ee-a4e3-36643a25b4bb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfShortTermDebt_01a063ef-fe70-7ce8-87ca-9d1c0993b483" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_RepaymentsOfShortTermDebt_01a063ef-fe70-7ce8-87ca-9d1c0993b483" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-fe70-7c02-ba7d-69bf87988071" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-fe70-7c02-ba7d-69bf87988071" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-fe70-7964-b2b3-f8c7f0a06e37" 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_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-fe70-7964-b2b3-f8c7f0a06e37" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_01a063ef-fe70-7081-85c2-e053a7d3782e" 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_01a063ef-fe70-7f10-8f33-829a7b0fa816" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_01a063ef-fe70-7081-85c2-e053a7d3782e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_01a063ef-fe70-749a-81a6-5662cd72f196" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_01a063ef-fe70-749a-81a6-5662cd72f196" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_01a063ef-fe70-7c32-bc12-12999230ddc1" 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_01a063ef-fe70-749a-81a6-5662cd72f196" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_01a063ef-fe70-7c32-bc12-12999230ddc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a063ef-fe70-7530-8d95-b49f7e75afef" 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_01a063ef-fe70-749a-81a6-5662cd72f196" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a063ef-fe70-7530-8d95-b49f7e75afef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_01a063ef-fe70-7164-a553-72278fc8f53b" 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_CashAndCashEquivalentsAtCarryingValueAbstract_01a063ef-fe70-749a-81a6-5662cd72f196" xlink:to="loc_us-gaap_InterestPaidNet_01a063ef-fe70-7164-a553-72278fc8f53b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_01a063ef-fe70-73b1-8b2b-42a6159d68c1" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_01a063ef-fe70-73b1-8b2b-42a6159d68c1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_01a063ef-fe70-7697-8b7c-40dfbeb101ce" 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_01a063ef-fe70-73b1-8b2b-42a6159d68c1" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_01a063ef-fe70-7697-8b7c-40dfbeb101ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_01a063ef-fe70-7051-8b12-c115048eb16f" 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_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_01a063ef-fe70-7051-8b12-c115048eb16f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_01a063ef-fe70-795c-af7f-e72e395c3c37" 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_StatementLineItems_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_01a063ef-fe70-795c-af7f-e72e395c3c37" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_01a063ef-fe70-73d1-bb54-5f7b88c2b7a7" 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_StatementLineItems_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_01a063ef-fe70-73d1-bb54-5f7b88c2b7a7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_01a063ef-fe70-7702-ae7c-08e31559b9cc" xlink:href="dpl-20260930.xsd#dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7bfa-a8c6-ef0a41b86db9" xlink:to="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_01a063ef-fe70-7702-ae7c-08e31559b9cc" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/StatementofShareholdersEquityStatement" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" 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_01a063ef-fe70-7f15-8c11-8c9eeaed300f" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_StatementTable_01a063ef-fe70-7f15-8c11-8c9eeaed300f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806" 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_01a063ef-fe70-7f15-8c11-8c9eeaed300f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806_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_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7be3-a417-46947f7af8ed" 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_01a063ef-fe70-7e4d-b8ec-bd2cc14b7806" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a063ef-fe70-7e28-9538-d0851933524e" 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_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_us-gaap_CommonStockMember_01a063ef-fe70-7e28-9538-d0851933524e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_01a063ef-fe70-714b-9c58-8ab39c40bd75" 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_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_01a063ef-fe70-714b-9c58-8ab39c40bd75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a063ef-fe70-72a9-af34-5d09a32d7a90" 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_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a063ef-fe70-72a9-af34-5d09a32d7a90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a063ef-fe70-70fb-8d51-e2cce606f91f" 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_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_us-gaap_RetainedEarningsMember_01a063ef-fe70-70fb-8d51-e2cce606f91f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a063ef-fe70-7944-ab60-dda4a99af6f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a063ef-fe70-7944-ab60-dda4a99af6f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CommonStockValueIssuedMember_01a063ef-fe70-7e71-81b0-608356f31f36" xlink:href="dpl-20260930.xsd#dpl_CommonStockValueIssuedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a063ef-fe70-7be3-a417-46947f7af8ed" xlink:to="loc_dpl_CommonStockValueIssuedMember_01a063ef-fe70-7e71-81b0-608356f31f36" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a179c0-0d22-70fe-bec5-3d3c9f023903" 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_01a063ef-fe70-7f15-8c11-8c9eeaed300f" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a179c0-0d22-70fe-bec5-3d3c9f023903" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a179c0-0d22-70fe-bec5-3d3c9f023903_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_01a179c0-0d22-70fe-bec5-3d3c9f023903" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a179c0-0d22-70fe-bec5-3d3c9f023903_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a179c0-0d22-7c8b-93d6-aa0a837de4eb" 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_01a179c0-0d22-70fe-bec5-3d3c9f023903" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a179c0-0d22-7c8b-93d6-aa0a837de4eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a179c0-0d22-70ad-9866-2d7d3811b88a" 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_01a179c0-0d22-7c8b-93d6-aa0a837de4eb" xlink:to="loc_srt_SubsidiariesMember_01a179c0-0d22-70ad-9866-2d7d3811b88a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_01a063ef-fe70-7cfd-b652-42ffe207faf2" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_SharesIssued_01a063ef-fe70-7cfd-b652-42ffe207faf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-764d-9b1d-88a8d497f78d" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-764d-9b1d-88a8d497f78d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfOrdinaryDividends_01a063ef-fe70-7269-9cd1-80be3e2f383b" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_PaymentsOfOrdinaryDividends_01a063ef-fe70-7269-9cd1-80be3e2f383b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-74c4-a634-6558918fa244" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_01a063ef-fe70-74c4-a634-6558918fa244" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_01a063ef-fe70-7c08-b3d9-a6074556ed20" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_StockholdersEquityOther_01a063ef-fe70-7c08-b3d9-a6074556ed20" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-796d-9777-b15a29a1ac22" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a063ef-fe70-796d-9777-b15a29a1ac22" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_01a063ef-fe70-780f-ad9a-bb09e721d281" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_PaymentsOfDividends_01a063ef-fe70-780f-ad9a-bb09e721d281" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-767c-9a9d-1cc001011405" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-fe70-767c-9a9d-1cc001011405" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-fe70-747d-8f66-027502e0db54" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-fe70-747d-8f66-027502e0db54" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a063ef-fe70-797a-90ba-9cbd78392ded" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_StockholdersEquity_01a063ef-fe70-797a-90ba-9cbd78392ded" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7b1c-8774-c56a43843d78" 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_01a063ef-fe70-77ee-9ce3-d6daca1726b5" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a063ef-fe70-7b1c-8774-c56a43843d78" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/OverviewandSummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-75a0-93f8-5da21701acf0" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-732c-9b02-46082fefa942" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-75a0-93f8-5da21701acf0" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-732c-9b02-46082fefa942" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantAccountingPoliciesTextBlock_01a063ef-fe70-7cfe-b640-32d7c69f5ef8" 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_01a063ef-fe70-75a0-93f8-5da21701acf0" xlink:to="loc_us-gaap_SignificantAccountingPoliciesTextBlock_01a063ef-fe70-7cfe-b640-32d7c69f5ef8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersNotes" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7a25-9688-e956b6b83d3b" 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_dpl_RegulatoryTable_01a063ef-fe70-7379-aed0-146c64990a0f" xlink:href="dpl-20260930.xsd#dpl_RegulatoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7a25-9688-e956b6b83d3b" xlink:to="loc_dpl_RegulatoryTable_01a063ef-fe70-7379-aed0-146c64990a0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_01a063ef-fe70-7ccf-8e0b-6365b3323ec9" 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_01a063ef-fe70-7a25-9688-e956b6b83d3b" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_01a063ef-fe70-7ccf-8e0b-6365b3323ec9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValue" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7365-b1a6-105f9c9663af" 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_01a063ef-ff17-785f-ae2b-4493586a8e97" 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_01a063ef-ff17-7365-b1a6-105f9c9663af" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a063ef-ff17-785f-ae2b-4493586a8e97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_01a063ef-ff17-7909-9884-c31234d6f1c5" 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_01a063ef-ff17-7365-b1a6-105f9c9663af" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_01a063ef-ff17-7909-9884-c31234d6f1c5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtObligations" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7f73-8f7a-c137fdaf65d2" 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_01a063ef-ff17-713b-9fc1-bb97dcb0774c" 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_01a063ef-ff17-7f73-8f7a-c137fdaf65d2" xlink:to="loc_us-gaap_DebtInstrumentTable_01a063ef-ff17-713b-9fc1-bb97dcb0774c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_01a063ef-ff17-7f68-8b7c-735e1eb47790" 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_01a063ef-ff17-7f73-8f7a-c137fdaf65d2" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_01a063ef-ff17-7f68-8b7c-735e1eb47790" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxes" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7f4c-a91d-ac080ef17802" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-7324-978f-81e86c18774a" 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_01a063ef-ff17-7f4c-a91d-ac080ef17802" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-7324-978f-81e86c18774a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7afb-b32a-2909fe314829" 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_01a063ef-ff17-7324-978f-81e86c18774a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7afb-b32a-2909fe314829" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7afb-b32a-2909fe314829_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_01a063ef-ff17-7afb-b32a-2909fe314829" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7afb-b32a-2909fe314829_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7249-9269-e4b127e0f20e" 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_01a063ef-ff17-7afb-b32a-2909fe314829" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7249-9269-e4b127e0f20e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7701-a79d-f2f2b0c8e570" 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_01a063ef-ff17-7249-9269-e4b127e0f20e" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7701-a79d-f2f2b0c8e570" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock_01a063ef-ff17-7b55-9b53-6798dd17373e" 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_01a063ef-ff17-7f4c-a91d-ac080ef17802" xlink:to="loc_us-gaap_IncomeTaxDisclosureTextBlock_01a063ef-ff17-7b55-9b53-6798dd17373e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlans" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7753-b0d5-380580611efc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-76fb-a9e3-92e243991b4a" 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_01a063ef-ff17-7753-b0d5-380580611efc" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-76fb-a9e3-92e243991b4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-76e0-80b2-817ed9ffe5cb" 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_01a063ef-ff17-76fb-a9e3-92e243991b4a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-76e0-80b2-817ed9ffe5cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-76e0-80b2-817ed9ffe5cb_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_01a063ef-ff17-76e0-80b2-817ed9ffe5cb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-76e0-80b2-817ed9ffe5cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-75de-a3cf-c558b29162df" 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_01a063ef-ff17-76e0-80b2-817ed9ffe5cb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-75de-a3cf-c558b29162df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7c44-96f0-a76144d039aa" 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_01a063ef-ff17-75de-a3cf-c558b29162df" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7c44-96f0-a76144d039aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_01a063ef-ff17-7340-aa91-d931c79523e8" 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_01a063ef-ff17-76fb-a9e3-92e243991b4a" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_01a063ef-ff17-7340-aa91-d931c79523e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7340-aa91-d931c79523e8_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_01a063ef-ff17-7340-aa91-d931c79523e8" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7340-aa91-d931c79523e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7ce8-a0af-33c705e51811" 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_01a063ef-ff17-7340-aa91-d931c79523e8" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7ce8-a0af-33c705e51811" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_01a063ef-ff17-74f1-8891-817ac4a52d22" 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_01a063ef-ff17-7ce8-a0af-33c705e51811" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_01a063ef-ff17-74f1-8891-817ac4a52d22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_01a063ef-ff17-79cb-966b-aefa462d219d" 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_01a063ef-ff17-7753-b0d5-380580611efc" xlink:to="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_01a063ef-ff17-79cb-966b-aefa462d219d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingencies" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-74f6-bf65-7f37e212db00" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-74ae-8c29-b143e7845595" 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_01a063ef-ff17-74f6-bf65-7f37e212db00" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-74ae-8c29-b143e7845595" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-78a3-94a6-d5a376dc07a7" 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_01a063ef-ff17-74ae-8c29-b143e7845595" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-78a3-94a6-d5a376dc07a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-78a3-94a6-d5a376dc07a7_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_01a063ef-ff17-78a3-94a6-d5a376dc07a7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-78a3-94a6-d5a376dc07a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d9c-b570-7311db29a046" 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_01a063ef-ff17-78a3-94a6-d5a376dc07a7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d9c-b570-7311db29a046" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7356-9004-e32514665bac" 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_01a063ef-ff17-7d9c-b570-7311db29a046" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7356-9004-e32514665bac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_01a063ef-ff17-7044-b74d-205f98eac079" 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_01a063ef-ff17-74f6-bf65-7f37e212db00" xlink:to="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_01a063ef-ff17-7044-b74d-205f98eac079" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegments" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-72a8-998b-a67029ade616" 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_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" 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_01a063ef-ff17-72a8-998b-a67029ade616" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ade-a54f-c6467e2dd9f1" 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_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ade-a54f-c6467e2dd9f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ade-a54f-c6467e2dd9f1_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_01a063ef-ff17-7ade-a54f-c6467e2dd9f1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ade-a54f-c6467e2dd9f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7540-9518-521f03b2a54e" 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_01a063ef-ff17-7ade-a54f-c6467e2dd9f1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7540-9518-521f03b2a54e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7ff1-8c4c-db3b1588d5b5" 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_01a063ef-ff17-7540-9518-521f03b2a54e" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7ff1-8c4c-db3b1588d5b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-755c-b26a-ebfb67c8fcd8" 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_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" xlink:to="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-755c-b26a-ebfb67c8fcd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-755c-b26a-ebfb67c8fcd8_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_01a063ef-ff17-755c-b26a-ebfb67c8fcd8" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-755c-b26a-ebfb67c8fcd8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-75ac-a8b8-6dc895677571" 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_01a063ef-ff17-755c-b26a-ebfb67c8fcd8" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-75ac-a8b8-6dc895677571" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_01a063ef-ff17-7e3e-955e-583972fc8d6b" 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_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" xlink:to="loc_us-gaap_SubsegmentsAxis_01a063ef-ff17-7e3e-955e-583972fc8d6b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7e3e-955e-583972fc8d6b_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_01a063ef-ff17-7e3e-955e-583972fc8d6b" xlink:to="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7e3e-955e-583972fc8d6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7b00-8a08-f9c2a68d434a" 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_01a063ef-ff17-7e3e-955e-583972fc8d6b" xlink:to="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7b00-8a08-f9c2a68d434a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a063ef-ff17-714e-923a-e3f027f232ab" 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_01a063ef-ff17-78c6-8ec8-2fcf02a10e1a" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a063ef-ff17-714e-923a-e3f027f232ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-714e-923a-e3f027f232ab_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_01a063ef-ff17-714e-923a-e3f027f232ab" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-714e-923a-e3f027f232ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-7db7-875d-67008bc81a7c" 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_01a063ef-ff17-714e-923a-e3f027f232ab" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-7db7-875d-67008bc81a7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_01a063ef-ff17-7103-ac14-062a78f3cf65" 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_01a063ef-ff17-72a8-998b-a67029ade616" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_01a063ef-ff17-7103-ac14-062a78f3cf65" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueNotes" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7d1d-8c3c-ea7f9d880a68" 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_DisaggregationOfRevenueTable_01a063ef-ff17-72f0-9fe3-78fdc4128205" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-7d1d-8c3c-ea7f9d880a68" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a063ef-ff17-72f0-9fe3-78fdc4128205" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ceb-b442-90652fc01dac" 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_DisaggregationOfRevenueTable_01a063ef-ff17-72f0-9fe3-78fdc4128205" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ceb-b442-90652fc01dac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ceb-b442-90652fc01dac_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_01a063ef-ff17-7ceb-b442-90652fc01dac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ceb-b442-90652fc01dac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-786a-b34b-85484159833a" 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_01a063ef-ff17-7ceb-b442-90652fc01dac" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-786a-b34b-85484159833a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-764b-9b64-c619fcda24e9" 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_01a063ef-ff17-786a-b34b-85484159833a" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-764b-9b64-c619fcda24e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_01a063ef-ff17-7fa5-92a9-17ef323fb39c" 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_01a063ef-ff17-7d1d-8c3c-ea7f9d880a68" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_01a063ef-ff17-7fa5-92a9-17ef323fb39c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperations" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-75a9-a22a-451479804a42" 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_01a063ef-ff17-78d7-bd01-261a0f16c68f" 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_01a063ef-ff17-75a9-a22a-451479804a42" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a063ef-ff17-78d7-bd01-261a0f16c68f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a063ef-ff17-7a9e-b7af-2cb35a86459f" 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_01a063ef-ff17-78d7-bd01-261a0f16c68f" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a063ef-ff17-7a9e-b7af-2cb35a86459f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-7a9e-b7af-2cb35a86459f_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_01a063ef-ff17-7a9e-b7af-2cb35a86459f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-7a9e-b7af-2cb35a86459f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-778f-bb3e-e0c9153d5f03" 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_01a063ef-ff17-7a9e-b7af-2cb35a86459f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-778f-bb3e-e0c9153d5f03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-774d-b51c-1ea8141ad3d5" 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_01a063ef-ff17-78d7-bd01-261a0f16c68f" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-774d-b51c-1ea8141ad3d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-774d-b51c-1ea8141ad3d5_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_01a063ef-ff17-774d-b51c-1ea8141ad3d5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-774d-b51c-1ea8141ad3d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7941-863a-f7a959f1cfdc" 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_01a063ef-ff17-774d-b51c-1ea8141ad3d5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7941-863a-f7a959f1cfdc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesPolicy" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-724c-8aae-11a5247bc724" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-724c-8aae-11a5247bc724" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryPolicyTextBlock_01a063ef-fe70-753b-a3b7-4e96234af320" 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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_us-gaap_InventoryPolicyTextBlock_01a063ef-fe70-753b-a3b7-4e96234af320" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NatureOfOperations_01a063ef-fe70-7a02-ac92-a69103f97083" 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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_us-gaap_NatureOfOperations_01a063ef-fe70-7a02-ac92-a69103f97083" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_01a063ef-fe70-7779-a337-24e8181f54fc" 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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_01a063ef-fe70-7779-a337-24e8181f54fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryIncomeTaxesPolicy_01a063ef-fe70-76e5-a1a1-5b9bd2c4dcd0" 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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_us-gaap_RegulatoryIncomeTaxesPolicy_01a063ef-fe70-76e5-a1a1-5b9bd2c4dcd0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_01a063ef-fe70-7d53-859a-67f9328a4cbf" 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_01a063ef-fe70-7f23-a3bd-c4e45f8c8e94" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_01a063ef-fe70-7d53-859a-67f9328a4cbf" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" 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_01a063ef-fe70-7a9e-aa5f-8310fc950142" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a063ef-fe70-7a9e-aa5f-8310fc950142" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_01a063ef-fe70-77b1-a8a4-6ecc10ca3144" xlink:href="dpl-20260930.xsd#dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_01a063ef-fe70-77b1-a8a4-6ecc10ca3144" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_01a063ef-fe70-7bfd-874a-65278b2fae75" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_01a063ef-fe70-7bfd-874a-65278b2fae75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_01a063ef-fe70-7b6a-8e1b-0b3b5c7849a3" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_01a063ef-fe70-7b6a-8e1b-0b3b5c7849a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_01a063ef-fe70-759a-9a0e-65aa6829a995" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_01a063ef-fe70-759a-9a0e-65aa6829a995" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_01a063ef-fe70-7513-9802-988c0119a7b2" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_01a063ef-fe70-7513-9802-988c0119a7b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_01a063ef-fe70-725d-98d3-d64cd3140611" 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_01a063ef-fe70-7f7f-9075-8eb2a2a565fe" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_01a063ef-fe70-725d-98d3-d64cd3140611" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-795a-a5a7-50a182f7e642" 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_01a063ef-ff17-706a-9b72-4b05267488b2" 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_01a063ef-ff17-795a-a5a7-50a182f7e642" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a063ef-ff17-706a-9b72-4b05267488b2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_01a063ef-ff17-7bd1-8876-63c6db86b8b3" 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_01a063ef-ff17-795a-a5a7-50a182f7e642" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_01a063ef-ff17-7bd1-8876-63c6db86b8b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_01a063ef-ff17-741f-8ef2-1861b6c05f35" 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_01a063ef-ff17-795a-a5a7-50a182f7e642" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_01a063ef-ff17-741f-8ef2-1861b6c05f35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_01a063ef-ff17-79e8-83f9-9586662b5b27" 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_01a063ef-ff17-795a-a5a7-50a182f7e642" xlink:to="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_01a063ef-ff17-79e8-83f9-9586662b5b27" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7aa5-83f0-baadd13ca63a" 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_01a063ef-ff17-749a-958f-536605a41c23" 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_01a063ef-ff17-7aa5-83f0-baadd13ca63a" xlink:to="loc_us-gaap_DebtInstrumentTable_01a063ef-ff17-749a-958f-536605a41c23" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_01a063ef-ff17-7e00-bbab-bc97c42b3116" 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_01a063ef-ff17-7aa5-83f0-baadd13ca63a" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_01a063ef-ff17-7e00-bbab-bc97c42b3116" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_01a063ef-ff17-7be8-99c9-47ac64f0fdcf" 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_01a063ef-ff17-7aa5-83f0-baadd13ca63a" xlink:to="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_01a063ef-ff17-7be8-99c9-47ac64f0fdcf" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7a89-9d39-8590bbc3d357" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-70b4-b54f-4812a38a684c" 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_01a063ef-ff17-7a89-9d39-8590bbc3d357" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-70b4-b54f-4812a38a684c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-713e-a301-7c517b69acf4" 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_01a063ef-ff17-70b4-b54f-4812a38a684c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-713e-a301-7c517b69acf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-713e-a301-7c517b69acf4_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_01a063ef-ff17-713e-a301-7c517b69acf4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-713e-a301-7c517b69acf4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d18-81cf-6d3a11813c31" 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_01a063ef-ff17-713e-a301-7c517b69acf4" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d18-81cf-6d3a11813c31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-74aa-9242-480e12b35876" 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_01a063ef-ff17-7d18-81cf-6d3a11813c31" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-74aa-9242-480e12b35876" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7ed7-9b48-137c98a57ff8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-7c51-828a-704183267f04" 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_01a063ef-ff17-7ed7-9b48-137c98a57ff8" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-7c51-828a-704183267f04" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7140-b81b-d850946c9f15" 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_01a063ef-ff17-7c51-828a-704183267f04" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7140-b81b-d850946c9f15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7140-b81b-d850946c9f15_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_01a063ef-ff17-7140-b81b-d850946c9f15" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7140-b81b-d850946c9f15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-778b-a917-5c527d575965" 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_01a063ef-ff17-7140-b81b-d850946c9f15" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-778b-a917-5c527d575965" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-79d2-a238-792a3279fdd7" 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_01a063ef-ff17-778b-a917-5c527d575965" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-79d2-a238-792a3279fdd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_01a063ef-ff17-7194-b8b2-3cdd0e47a54f" xlink:href="dpl-20260930.xsd#dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_01a063ef-ff17-7ed7-9b48-137c98a57ff8" xlink:to="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_01a063ef-ff17-7194-b8b2-3cdd0e47a54f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7cff-8554-126941849c2f" 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_01a063ef-ff17-7f17-9977-84aec1093fb9" 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_01a063ef-ff17-7cff-8554-126941849c2f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a063ef-ff17-7f17-9977-84aec1093fb9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-71d3-a720-2c42ca3ac24b" 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_01a063ef-ff17-7f17-9977-84aec1093fb9" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-71d3-a720-2c42ca3ac24b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-71d3-a720-2c42ca3ac24b_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_01a063ef-ff17-71d3-a720-2c42ca3ac24b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-71d3-a720-2c42ca3ac24b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-76e6-ba58-9ee341d3da48" 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_01a063ef-ff17-71d3-a720-2c42ca3ac24b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-76e6-ba58-9ee341d3da48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-706a-8a55-3dd0281feb62" 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_01a063ef-ff17-76e6-ba58-9ee341d3da48" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-706a-8a55-3dd0281feb62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7e44-9780-8e51663c67a1" 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_01a063ef-ff17-7f17-9977-84aec1093fb9" xlink:to="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7e44-9780-8e51663c67a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7e44-9780-8e51663c67a1_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_01a063ef-ff17-7e44-9780-8e51663c67a1" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7e44-9780-8e51663c67a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7c02-aa0b-37ff311c53ed" 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_01a063ef-ff17-7e44-9780-8e51663c67a1" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7c02-aa0b-37ff311c53ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_01a063ef-ff17-7ddb-b22b-d77cd97cad5c" 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_01a063ef-ff17-7f17-9977-84aec1093fb9" xlink:to="loc_us-gaap_SubsegmentsAxis_01a063ef-ff17-7ddb-b22b-d77cd97cad5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7ddb-b22b-d77cd97cad5c_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_01a063ef-ff17-7ddb-b22b-d77cd97cad5c" xlink:to="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7ddb-b22b-d77cd97cad5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7469-a41e-443b0ef2d1d4" 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_01a063ef-ff17-7ddb-b22b-d77cd97cad5c" xlink:to="loc_us-gaap_SubsegmentsDomain_01a063ef-ff17-7469-a41e-443b0ef2d1d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a063ef-ff17-79fe-8526-53d37711a3b4" 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_01a063ef-ff17-7f17-9977-84aec1093fb9" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_01a063ef-ff17-79fe-8526-53d37711a3b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-79fe-8526-53d37711a3b4_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_01a063ef-ff17-79fe-8526-53d37711a3b4" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-79fe-8526-53d37711a3b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-7a84-a357-e988292ca146" 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_01a063ef-ff17-79fe-8526-53d37711a3b4" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_01a063ef-ff17-7a84-a357-e988292ca146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_01a063ef-ff17-7a85-b46c-2354942a9f32" 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_01a063ef-ff17-7cff-8554-126941849c2f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_01a063ef-ff17-7a85-b46c-2354942a9f32" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-735e-9213-ecca3be9cb6e" 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_01a063ef-ff17-7f4c-ad8e-9ca8c108e783" 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_01a063ef-ff17-735e-9213-ecca3be9cb6e" xlink:to="loc_us-gaap_StatementTable_01a063ef-ff17-7f4c-ad8e-9ca8c108e783" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7d70-915c-9b93a3b2523b" 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_01a063ef-ff17-7f4c-ad8e-9ca8c108e783" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7d70-915c-9b93a3b2523b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d70-915c-9b93a3b2523b_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_01a063ef-ff17-7d70-915c-9b93a3b2523b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d70-915c-9b93a3b2523b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7228-9f1d-a680f7a6d6de" 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_01a063ef-ff17-7d70-915c-9b93a3b2523b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7228-9f1d-a680f7a6d6de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-76b2-b4e9-12a66177d500" 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_01a063ef-ff17-7228-9f1d-a680f7a6d6de" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-76b2-b4e9-12a66177d500" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_01a063ef-ff17-77f4-859d-b723fa91306e" 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_01a063ef-ff17-735e-9213-ecca3be9cb6e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_01a063ef-ff17-77f4-859d-b723fa91306e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsTables" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-78bb-af13-69d03c10a26b" 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_01a063ef-ff17-7d35-94cd-ef262f50ef75" 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_01a063ef-ff17-78bb-af13-69d03c10a26b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a063ef-ff17-7d35-94cd-ef262f50ef75" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a063ef-ff17-7015-85bc-c4a68d6cf75f" 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_01a063ef-ff17-7d35-94cd-ef262f50ef75" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a063ef-ff17-7015-85bc-c4a68d6cf75f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-7015-85bc-c4a68d6cf75f_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_01a063ef-ff17-7015-85bc-c4a68d6cf75f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-7015-85bc-c4a68d6cf75f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-73b3-86a5-01e3132509d1" 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_01a063ef-ff17-7015-85bc-c4a68d6cf75f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a063ef-ff17-73b3-86a5-01e3132509d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-7e58-9938-5a33a09facab" 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_01a063ef-ff17-7d35-94cd-ef262f50ef75" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-7e58-9938-5a33a09facab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e58-9938-5a33a09facab_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_01a063ef-ff17-7e58-9938-5a33a09facab" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e58-9938-5a33a09facab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e20-a09e-4a42a8d46d0c" 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_01a063ef-ff17-7e58-9938-5a33a09facab" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e20-a09e-4a42a8d46d0c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-7b4a-83ad-410be716c9a3" xlink:href="dpl-20260930.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_01a063ef-fe70-7b4a-83ad-410be716c9a3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a063ef-fe70-7b79-9e4c-5f5154e98ac7" 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_01a063ef-fe70-7b4a-83ad-410be716c9a3" xlink:to="loc_us-gaap_CreditFacilityAxis_01a063ef-fe70-7b79-9e4c-5f5154e98ac7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a063ef-fe70-7b79-9e4c-5f5154e98ac7_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_01a063ef-fe70-7b79-9e4c-5f5154e98ac7" xlink:to="loc_us-gaap_CreditFacilityDomain_01a063ef-fe70-7b79-9e4c-5f5154e98ac7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a063ef-fe70-7339-a0f1-4be12291784a" 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_01a063ef-fe70-7b79-9e4c-5f5154e98ac7" xlink:to="loc_us-gaap_CreditFacilityDomain_01a063ef-fe70-7339-a0f1-4be12291784a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a063ef-fe70-70bb-9655-bea3ccf01a04" 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_01a063ef-fe70-7b4a-83ad-410be716c9a3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a063ef-fe70-70bb-9655-bea3ccf01a04" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a063ef-fe70-70bb-9655-bea3ccf01a04_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_01a063ef-fe70-70bb-9655-bea3ccf01a04" xlink:to="loc_us-gaap_RelatedPartyDomain_01a063ef-fe70-70bb-9655-bea3ccf01a04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a063ef-fe70-7b6d-b880-6aa44f800832" 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_01a063ef-fe70-70bb-9655-bea3ccf01a04" xlink:to="loc_us-gaap_RelatedPartyDomain_01a063ef-fe70-7b6d-b880-6aa44f800832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_01a063ef-fe70-77aa-a54b-e9f3d6e68c03" 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_01a063ef-fe70-7b6d-b880-6aa44f800832" xlink:to="loc_us-gaap_NonrelatedPartyMember_01a063ef-fe70-77aa-a54b-e9f3d6e68c03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a063ef-fe70-7ee6-9431-564aa08b09a9" 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_01a063ef-fe70-7b6d-b880-6aa44f800832" xlink:to="loc_us-gaap_RelatedPartyMember_01a063ef-fe70-7ee6-9431-564aa08b09a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_01a063ef-fe70-7694-a27a-3116dcd0cfbe" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_NumberOfReportableSegments_01a063ef-fe70-7694-a27a-3116dcd0cfbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-7b0e-8874-9978374887ae" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a063ef-fe70-7b0e-8874-9978374887ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_01a063ef-fe70-7f06-b59c-7986119d92b0" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_RestrictedCash_01a063ef-fe70-7f06-b59c-7986119d92b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_01a063ef-fe70-756a-83df-90eb4679f450" xlink:href="dpl-20260930.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_NumberOfRetailCustomers_01a063ef-fe70-756a-83df-90eb4679f450" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_01a063ef-fe70-7560-9ac3-9aefd9707095" xlink:href="dpl-20260930.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_ServiceAreaSquareMiles_01a063ef-fe70-7560-9ac3-9aefd9707095" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_01a063ef-fe70-79e5-8b5a-93c4760747f7" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_NumberOfOperatingSegments_01a063ef-fe70-79e5-8b5a-93c4760747f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExciseTaxesCollected_01a063ef-fe70-730e-831b-a60efd1babed" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_ExciseTaxesCollected_01a063ef-fe70-730e-831b-a60efd1babed" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CustomerReceivables_01a063ef-fe70-7f37-a3cc-af0ff549e2eb" xlink:href="dpl-20260930.xsd#dpl_CustomerReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_CustomerReceivables_01a063ef-fe70-7f37-a3cc-af0ff549e2eb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UnbilledRevenue_01a063ef-fe70-7b95-8cdf-fd8be87b6d66" xlink:href="dpl-20260930.xsd#dpl_UnbilledRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_UnbilledRevenue_01a063ef-fe70-7b95-8cdf-fd8be87b6d66" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivables_01a063ef-fe70-7b83-9736-7f9e7126cbd0" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_OtherReceivables_01a063ef-fe70-7b83-9736-7f9e7126cbd0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_01a063ef-fe70-789a-862b-1e502573dfb8" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_01a063ef-fe70-789a-862b-1e502573dfb8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a063ef-fe70-7fbc-a10a-13f45426b8b5" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_01a063ef-fe70-7fbc-a10a-13f45426b8b5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_01a063ef-fe70-72ca-872a-c3eec7f6604b" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_01a063ef-fe70-72ca-872a-c3eec7f6604b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_01a063ef-fe70-7c75-a9ab-4b3cb64620e6" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_01a063ef-fe70-7c75-a9ab-4b3cb64620e6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_01a063ef-fe70-74e0-b057-1bb4c187b71d" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_01a063ef-fe70-74e0-b057-1bb4c187b71d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_01a063ef-fe70-7767-98fb-a546573e09f6" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_InterestAndDebtExpense_01a063ef-fe70-7767-98fb-a546573e09f6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-fe70-74c0-aaea-8335a44c42b9" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-fe70-74c0-aaea-8335a44c42b9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_01a063ef-fe70-7cd2-aecd-0d9d2bf1c6dc" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_01a063ef-fe70-7cd2-aecd-0d9d2bf1c6dc" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7344-9955-6e547300852e" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7344-9955-6e547300852e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7908-ba12-243d6ff3b009" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a063ef-fe70-7908-ba12-243d6ff3b009" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-fe70-7900-bbbc-5574fadd88d4" 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_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-fe70-7900-bbbc-5574fadd88d4" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_01a063ef-fe70-7cb5-a9ec-ef6a3cf45407" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_01a063ef-fe70-7cb5-a9ec-ef6a3cf45407" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a063ef-fe70-77eb-a1bd-501a4b3d6a18" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a063ef-fe70-77eb-a1bd-501a4b3d6a18" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-7747-90d3-13cfb433e661" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_01a063ef-fe70-7747-90d3-13cfb433e661" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_01a063ef-fe70-76cb-b908-dfb0fee2beee" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_01a063ef-fe70-76cb-b908-dfb0fee2beee" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_01a063ef-fe70-740e-8f9a-c3274246fac9" xlink:href="dpl-20260930.xsd#dpl_AllowanceForFundsUsedDuringConstructionEquityPortion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_01a063ef-fe70-740e-8f9a-c3274246fac9" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_01a063ef-fe70-7c95-a9a6-5e067e02ab56" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_01a063ef-fe70-7c95-a9a6-5e067e02ab56" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_01a063ef-fe70-70a9-bb59-5b8f9be64cdc" 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_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_01a063ef-fe70-70a9-bb59-5b8f9be64cdc" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsInvestmentPercent_01a063ef-fe70-7d38-acb7-9ebbf95d636a" xlink:href="dpl-20260930.xsd#dpl_OhioHoldingsInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_OhioHoldingsInvestmentPercent_01a063ef-fe70-7d38-acb7-9ebbf95d636a" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentPercent_01a063ef-fe70-74f9-87cd-194d2bc4ec6d" xlink:href="dpl-20260930.xsd#dpl_CDPQInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_01a063ef-fe70-7e17-986a-24eecdc93f22" xlink:to="loc_dpl_CDPQInvestmentPercent_01a063ef-fe70-74f9-87cd-194d2bc4ec6d" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a063ef-fe70-767c-a8c8-67c292bf9181" 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_01a063ef-fe70-754e-bb3a-7b52b9dc3d07" 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_01a063ef-fe70-767c-a8c8-67c292bf9181" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_01a063ef-fe70-754e-bb3a-7b52b9dc3d07" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-fe70-7804-9994-21f316c574c2" 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_ScheduleOfPropertyPlantAndEquipmentTable_01a063ef-fe70-754e-bb3a-7b52b9dc3d07" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-fe70-7804-9994-21f316c574c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7804-9994-21f316c574c2_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_01a063ef-fe70-7804-9994-21f316c574c2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7804-9994-21f316c574c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7894-8f24-cba482a934e1" 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_01a063ef-fe70-7804-9994-21f316c574c2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-fe70-7894-8f24-cba482a934e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-fe70-7a8d-ab16-32f1e3ca8ecf" 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_01a063ef-fe70-7894-8f24-cba482a934e1" xlink:to="loc_srt_SubsidiariesMember_01a063ef-fe70-7a8d-ab16-32f1e3ca8ecf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a063ef-fe70-7f17-945b-75c13235535a" 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_01a063ef-fe70-767c-a8c8-67c292bf9181" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_01a063ef-fe70-7f17-945b-75c13235535a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_01a063ef-fe70-7a45-bc95-96e516f721fb" 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_01a063ef-fe70-767c-a8c8-67c292bf9181" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_01a063ef-fe70-7a45-bc95-96e516f721fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContributionsInAidOfConstruction_01a179c8-813a-7116-b1c9-2142ef4d4711" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContributionsInAidOfConstruction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_01a063ef-fe70-767c-a8c8-67c292bf9181" xlink:to="loc_us-gaap_ContributionsInAidOfConstruction_01a179c8-813a-7116-b1c9-2142ef4d4711" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-fe70-7b78-9480-4395ac423b28" 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_dpl_RegulatoryNotesTable_01a063ef-fe70-7105-911f-644b905837c0" xlink:href="dpl-20260930.xsd#dpl_RegulatoryNotesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RegulatoryNotesTable_01a063ef-fe70-7105-911f-644b905837c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7e72-8237-e85b0049f9bf" 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_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_01a063ef-fe70-7e72-8237-e85b0049f9bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_01a063ef-fe70-7d7b-86fd-e83af5fa7f0c" 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_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_01a063ef-fe70-7d7b-86fd-e83af5fa7f0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilities_01a063ef-fe70-7e32-b822-edb3942179f4" 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_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_us-gaap_RegulatoryLiabilities_01a063ef-fe70-7e32-b822-edb3942179f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueRequirementThreeYearRatePlan2027_01a063ef-fe70-7990-9480-d6fdcdd2918a" xlink:href="dpl-20260930.xsd#dpl_RevenueRequirementThreeYearRatePlan2027"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RevenueRequirementThreeYearRatePlan2027_01a063ef-fe70-7990-9480-d6fdcdd2918a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueRequirementThreeYearRatePlan2028_01a063ef-fe70-7da7-b351-cc1bffdef933" xlink:href="dpl-20260930.xsd#dpl_RevenueRequirementThreeYearRatePlan2028"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RevenueRequirementThreeYearRatePlan2028_01a063ef-fe70-7da7-b351-cc1bffdef933" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueRequirementThreeYearRatePlan2029_01a063ef-fe70-789b-8699-fef5d89f4ff0" xlink:href="dpl-20260930.xsd#dpl_RevenueRequirementThreeYearRatePlan2029"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RevenueRequirementThreeYearRatePlan2029_01a063ef-fe70-789b-8699-fef5d89f4ff0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityThreeYearRatePlan_01a063ef-fe70-7885-afc3-e92f48158a60" xlink:href="dpl-20260930.xsd#dpl_ReturnOnEquityThreeYearRatePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_ReturnOnEquityThreeYearRatePlan_01a063ef-fe70-7885-afc3-e92f48158a60" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2027_01a063ef-fe70-7014-9cc8-506f47564f02" xlink:href="dpl-20260930.xsd#dpl_CostOfLongTermDebtThreeYearRatePlan2027"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2027_01a063ef-fe70-7014-9cc8-506f47564f02" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2028_01a063ef-fe70-7289-821f-bf641a27a722" xlink:href="dpl-20260930.xsd#dpl_CostOfLongTermDebtThreeYearRatePlan2028"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2028_01a063ef-fe70-7289-821f-bf641a27a722" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2029_01a063ef-fe70-7083-8ceb-fda137341492" xlink:href="dpl-20260930.xsd#dpl_CostOfLongTermDebtThreeYearRatePlan2029"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CostOfLongTermDebtThreeYearRatePlan2029_01a063ef-fe70-7083-8ceb-fda137341492" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseThreeYearRatePlan2027_01a063ef-fe70-757a-877e-9ba47049619e" xlink:href="dpl-20260930.xsd#dpl_RateBaseThreeYearRatePlan2027"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RateBaseThreeYearRatePlan2027_01a063ef-fe70-757a-877e-9ba47049619e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseThreeYearRatePlan2028_01a063ef-fe70-7c64-8067-93612d13da32" xlink:href="dpl-20260930.xsd#dpl_RateBaseThreeYearRatePlan2028"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RateBaseThreeYearRatePlan2028_01a063ef-fe70-7c64-8067-93612d13da32" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseThreeYearRatePlan2029_01a063ef-ff17-7168-a501-330d3a5aa6de" xlink:href="dpl-20260930.xsd#dpl_RateBaseThreeYearRatePlan2029"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_RateBaseThreeYearRatePlan2029_01a063ef-ff17-7168-a501-330d3a5aa6de" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityThreeYearRatePlan2027_01a063ef-ff17-7da8-83ed-bc94c65318ec" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureEquityThreeYearRatePlan2027"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureEquityThreeYearRatePlan2027_01a063ef-ff17-7da8-83ed-bc94c65318ec" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2027_01a063ef-ff17-7a43-871f-dcd64a6dfbd1" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureLongTermDebtThreeYearRatePlan2027"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2027_01a063ef-ff17-7a43-871f-dcd64a6dfbd1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityThreeYearRatePlan2028_01a063ef-ff17-704e-8287-f4a7bb3678de" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureEquityThreeYearRatePlan2028"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureEquityThreeYearRatePlan2028_01a063ef-ff17-704e-8287-f4a7bb3678de" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2028_01a063ef-ff17-7628-8c2c-180759b32cb0" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureLongTermDebtThreeYearRatePlan2028"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2028_01a063ef-ff17-7628-8c2c-180759b32cb0" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityThreeYearRatePlan2029_01a063ef-ff17-7066-90ab-d3a28fec162c" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureEquityThreeYearRatePlan2029"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureEquityThreeYearRatePlan2029_01a063ef-ff17-7066-90ab-d3a28fec162c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2029_01a063ef-ff17-7ba6-b388-ecf3968d2a26" xlink:href="dpl-20260930.xsd#dpl_CapitalStructureLongTermDebtThreeYearRatePlan2029"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-fe70-7b78-9480-4395ac423b28" xlink:to="loc_dpl_CapitalStructureLongTermDebtThreeYearRatePlan2029_01a063ef-ff17-7ba6-b388-ecf3968d2a26" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_01a17e0c-7fc4-79c8-a5f1-5adb7d68eca5" 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_01a063ef-ff17-762e-a882-4af119815102" 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_01a17e0c-7fc4-79c8-a5f1-5adb7d68eca5" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_01a063ef-ff17-762e-a882-4af119815102" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RSCRider_01a17e0c-d4f4-70af-8dbb-2a96b6500dc0" xlink:href="dpl-20260930.xsd#dpl_RSCRider"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_01a17e0c-7fc4-79c8-a5f1-5adb7d68eca5" xlink:to="loc_dpl_RSCRider_01a17e0c-d4f4-70af-8dbb-2a96b6500dc0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7ebd-9bd7-c54ba988f092" 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_01a063ef-ff17-7928-bcc9-f32f9c5e4421" 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_01a063ef-ff17-7ebd-9bd7-c54ba988f092" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_01a063ef-ff17-7928-bcc9-f32f9c5e4421" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-70ba-bcd3-ff09a906f6e1" 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_01a063ef-ff17-7928-bcc9-f32f9c5e4421" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-70ba-bcd3-ff09a906f6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-70ba-bcd3-ff09a906f6e1_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_01a063ef-ff17-70ba-bcd3-ff09a906f6e1" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-70ba-bcd3-ff09a906f6e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7f9a-b2cd-42ef01e1dbaa" 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_01a063ef-ff17-70ba-bcd3-ff09a906f6e1" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7f9a-b2cd-42ef01e1dbaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7f33-95c9-15c337142f96" 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_01a063ef-ff17-7f9a-b2cd-42ef01e1dbaa" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7f33-95c9-15c337142f96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-7ee3-9cbb-e9667caf2306" 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_01a063ef-ff17-7f9a-b2cd-42ef01e1dbaa" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-7ee3-9cbb-e9667caf2306" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a063ef-ff17-7ece-b54e-315b1a0c9411" 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_01a063ef-ff17-7928-bcc9-f32f9c5e4421" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a063ef-ff17-7ece-b54e-315b1a0c9411" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-7ece-b54e-315b1a0c9411_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_01a063ef-ff17-7ece-b54e-315b1a0c9411" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-7ece-b54e-315b1a0c9411_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-71fa-9826-8c89f7e7b2a0" 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_01a063ef-ff17-7ece-b54e-315b1a0c9411" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-71fa-9826-8c89f7e7b2a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a063ef-ff17-7ebb-b8a0-b519297e49d9" 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_01a063ef-ff17-71fa-9826-8c89f7e7b2a0" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a063ef-ff17-7ebb-b8a0-b519297e49d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a063ef-ff17-7a67-a64f-a163fdfcc571" 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_01a063ef-ff17-71fa-9826-8c89f7e7b2a0" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a063ef-ff17-7a67-a64f-a163fdfcc571" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a063ef-ff17-7e14-b960-56a8923e3801" 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_01a063ef-ff17-71fa-9826-8c89f7e7b2a0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a063ef-ff17-7e14-b960-56a8923e3801" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-7cc8-b949-2f25c1f7f8da" 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_01a063ef-ff17-7928-bcc9-f32f9c5e4421" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-7cc8-b949-2f25c1f7f8da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-7cc8-b949-2f25c1f7f8da_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_01a063ef-ff17-7cc8-b949-2f25c1f7f8da" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-7cc8-b949-2f25c1f7f8da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-7c51-a33e-2eb93ac26c87" 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_01a063ef-ff17-7cc8-b949-2f25c1f7f8da" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-7c51-a33e-2eb93ac26c87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7a9a-8a8a-b3c902dea242" 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_01a063ef-ff17-7c51-a33e-2eb93ac26c87" xlink:to="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7a9a-8a8a-b3c902dea242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_01a063ef-ff17-758d-9652-f7ca3811d5b8" 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_01a063ef-ff17-7c51-a33e-2eb93ac26c87" xlink:to="loc_us-gaap_DebtMember_01a063ef-ff17-758d-9652-f7ca3811d5b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-706c-8c5e-9bb1d3b784ba" 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_01a063ef-ff17-7ebd-9bd7-c54ba988f092" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-706c-8c5e-9bb1d3b784ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_01a063ef-ff17-7a0d-add2-330b986769b8" 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_01a063ef-ff17-7ebd-9bd7-c54ba988f092" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_01a063ef-ff17-7a0d-add2-330b986769b8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueandCostofNonDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7085-b449-08354a5d4901" 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_01a063ef-ff17-7cc2-9cf9-fa55ce17292d" 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_01a063ef-ff17-7085-b449-08354a5d4901" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_01a063ef-ff17-7cc2-9cf9-fa55ce17292d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-72c3-9827-f290b544a102" 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_01a063ef-ff17-7cc2-9cf9-fa55ce17292d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-72c3-9827-f290b544a102" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-72c3-9827-f290b544a102_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_01a063ef-ff17-72c3-9827-f290b544a102" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-72c3-9827-f290b544a102_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-74e4-af08-7c052b853004" 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_01a063ef-ff17-72c3-9827-f290b544a102" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-74e4-af08-7c052b853004" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7edd-8cbb-8ea887736274" 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_01a063ef-ff17-74e4-af08-7c052b853004" xlink:to="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7edd-8cbb-8ea887736274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_01a063ef-ff17-7422-9cbb-0d715c742f0c" 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_01a063ef-ff17-74e4-af08-7c052b853004" xlink:to="loc_us-gaap_DebtMember_01a063ef-ff17-7422-9cbb-0d715c742f0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-7897-9b18-820eaf48309f" 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_01a063ef-ff17-7cc2-9cf9-fa55ce17292d" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-7897-9b18-820eaf48309f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7897-9b18-820eaf48309f_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_01a063ef-ff17-7897-9b18-820eaf48309f" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7897-9b18-820eaf48309f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7727-bde2-015b99e0969c" 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_01a063ef-ff17-7897-9b18-820eaf48309f" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7727-bde2-015b99e0969c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7bbe-bd14-0ec0a1dd4a59" 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_01a063ef-ff17-7727-bde2-015b99e0969c" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7bbe-bd14-0ec0a1dd4a59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-7cbc-a1ef-daf13c060d2d" 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_01a063ef-ff17-7727-bde2-015b99e0969c" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-7cbc-a1ef-daf13c060d2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a063ef-ff17-7f29-bc93-742cfd3f5e12" 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_01a063ef-ff17-7085-b449-08354a5d4901" xlink:to="loc_us-gaap_LongTermDebt_01a063ef-ff17-7f29-bc93-742cfd3f5e12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-7e59-af97-0d76ebc4106b" 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_01a063ef-ff17-7085-b449-08354a5d4901" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-7e59-af97-0d76ebc4106b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" 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_01a063ef-ff17-71e7-b987-fee64963a571" 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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_01a063ef-ff17-71e7-b987-fee64963a571" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-72d6-9491-73fd0b943398" 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_01a063ef-ff17-71e7-b987-fee64963a571" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_01a063ef-ff17-72d6-9491-73fd0b943398" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-72d6-9491-73fd0b943398_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_01a063ef-ff17-72d6-9491-73fd0b943398" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-72d6-9491-73fd0b943398_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-782d-9c39-80d224111a89" 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_01a063ef-ff17-72d6-9491-73fd0b943398" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_01a063ef-ff17-782d-9c39-80d224111a89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7c76-a146-d2ac3e4c7e6d" 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_01a063ef-ff17-782d-9c39-80d224111a89" xlink:to="loc_us-gaap_MoneyMarketFundsMember_01a063ef-ff17-7c76-a146-d2ac3e4c7e6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_01a063ef-ff17-7233-add6-6219a4ffe376" 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_01a063ef-ff17-782d-9c39-80d224111a89" xlink:to="loc_us-gaap_DebtMember_01a063ef-ff17-7233-add6-6219a4ffe376" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_01a063ef-ff17-75fe-9565-989c87ed91aa" 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_01a063ef-ff17-782d-9c39-80d224111a89" xlink:to="loc_us-gaap_MutualFundMember_01a063ef-ff17-75fe-9565-989c87ed91aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-7732-bce4-e4e69b72cc81" 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_01a063ef-ff17-71e7-b987-fee64963a571" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a063ef-ff17-7732-bce4-e4e69b72cc81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7732-bce4-e4e69b72cc81_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_01a063ef-ff17-7732-bce4-e4e69b72cc81" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7732-bce4-e4e69b72cc81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7562-99d7-8b44471cf585" 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_01a063ef-ff17-7732-bce4-e4e69b72cc81" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a063ef-ff17-7562-99d7-8b44471cf585" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7891-8148-4c916f74d61f" 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_01a063ef-ff17-7562-99d7-8b44471cf585" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a063ef-ff17-7891-8148-4c916f74d61f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-79e4-a9f9-3b127a79bddd" 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_01a063ef-ff17-7891-8148-4c916f74d61f" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a063ef-ff17-79e4-a9f9-3b127a79bddd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a063ef-ff17-75c8-8c9d-2b3e313a89bc" 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_01a063ef-ff17-71e7-b987-fee64963a571" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a063ef-ff17-75c8-8c9d-2b3e313a89bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-75c8-8c9d-2b3e313a89bc_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_01a063ef-ff17-75c8-8c9d-2b3e313a89bc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-75c8-8c9d-2b3e313a89bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-711b-9c1f-cf682771e15e" 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_01a063ef-ff17-75c8-8c9d-2b3e313a89bc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a063ef-ff17-711b-9c1f-cf682771e15e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a063ef-ff17-77e2-89b3-f1e950567ded" 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_01a063ef-ff17-711b-9c1f-cf682771e15e" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a063ef-ff17-77e2-89b3-f1e950567ded" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a063ef-ff17-7107-8c83-88b6a6643216" 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_01a063ef-ff17-711b-9c1f-cf682771e15e" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a063ef-ff17-7107-8c83-88b6a6643216" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a063ef-ff17-7fa1-bd78-d744edabd9b8" 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_01a063ef-ff17-711b-9c1f-cf682771e15e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a063ef-ff17-7fa1-bd78-d744edabd9b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_01a063ef-ff17-7e1c-87ee-df75bb0177f2" 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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_DebtInstrumentFairValue_01a063ef-ff17-7e1c-87ee-df75bb0177f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-79b5-9c30-ce8f493449dd" 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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_01a063ef-ff17-79b5-9c30-ce8f493449dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_01a063ef-ff17-7f96-b045-55d9248dbb64" 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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_01a063ef-ff17-7f96-b045-55d9248dbb64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a063ef-ff17-7c0e-b940-ac5c5abdabff" 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_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_LongTermDebt_01a063ef-ff17-7c0e-b940-ac5c5abdabff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a063ef-ff17-7bd9-856e-62a49aef630c" 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_StatementLineItems_01a063ef-ff17-7d49-b4bd-9a09faed0eb5" xlink:to="loc_us-gaap_LineOfCredit_01a063ef-ff17-7bd9-856e-62a49aef630c" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" 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_01a063ef-ff17-7ebc-b5b2-e2e3efe20a3d" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_DebtInstrumentTable_01a063ef-ff17-7ebc-b5b2-e2e3efe20a3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7324-8447-72512e13f638" 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_01a063ef-ff17-7ebc-b5b2-e2e3efe20a3d" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7324-8447-72512e13f638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7324-8447-72512e13f638_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_01a063ef-ff17-7324-8447-72512e13f638" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7324-8447-72512e13f638_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" 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_01a063ef-ff17-7324-8447-72512e13f638" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_01a063ef-ff17-7e15-81fc-c97fc1599b2e" xlink:href="dpl-20260930.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_01a063ef-ff17-7e15-81fc-c97fc1599b2e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a063ef-ff17-7465-85ba-e4fef53824d2" 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_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a063ef-ff17-7465-85ba-e4fef53824d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_01a063ef-ff17-71b5-be2e-dc8cbd53617a" xlink:href="dpl-20260930.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_01a063ef-ff17-71b5-be2e-dc8cbd53617a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_01a063ef-ff17-7506-a52f-6c9e56c82a29" xlink:href="dpl-20260930.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_01a063ef-ff17-7506-a52f-6c9e56c82a29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-73e7-970a-7a483142ce8f" xlink:href="dpl-20260930.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-73e7-970a-7a483142ce8f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-7443-8712-38784944ab5f" xlink:href="dpl-20260930.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-7443-8712-38784944ab5f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49FirstMortgageBondsDue2028Member_01a063ef-ff17-742b-b71d-c32ee3f993ae" xlink:href="dpl-20260930.xsd#dpl_A5.49FirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A5.49FirstMortgageBondsDue2028Member_01a063ef-ff17-742b-b71d-c32ee3f993ae" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49SeniorNotesDue2028Member_01a063ef-ff17-7064-968e-9f174c3c5678" xlink:href="dpl-20260930.xsd#dpl_A5.49SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A5.49SeniorNotesDue2028Member_01a063ef-ff17-7064-968e-9f174c3c5678" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.55FirstMortgageBondDue2030Member_01a063ef-ff17-72f2-8db1-b5aeed547289" xlink:href="dpl-20260930.xsd#dpl_A4.55FirstMortgageBondDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A4.55FirstMortgageBondDue2030Member_01a063ef-ff17-72f2-8db1-b5aeed547289" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_01a063ef-ff17-75f9-a6c6-3ee223fffd2a" xlink:href="dpl-20260930.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_01a063ef-ff17-75f9-a6c6-3ee223fffd2a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_01a063ef-ff17-7b7a-9794-a7b0c23bd77b" xlink:href="dpl-20260930.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-768c-883d-733587c54c92" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_01a063ef-ff17-7b7a-9794-a7b0c23bd77b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a063ef-ff17-739d-8b19-d9ec6fb743fe" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_LineOfCredit_01a063ef-ff17-739d-8b19-d9ec6fb743fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a063ef-ff17-7b0b-b2dc-30a644c22eb3" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a063ef-ff17-7b0b-b2dc-30a644c22eb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_01a063ef-ff17-702d-b4bd-a1f013a85edf" xlink:href="dpl-20260930.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_01a063ef-ff17-702d-b4bd-a1f013a85edf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-ff17-76d3-9737-35613bb31a9f" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-ff17-76d3-9737-35613bb31a9f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a063ef-ff17-773a-b406-9359be7e81db" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a063ef-ff17-773a-b406-9359be7e81db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_01a063ef-ff17-7f9c-8dab-04411aeacad1" xlink:href="dpl-20260930.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_01a063ef-ff17-7f9c-8dab-04411aeacad1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_01a063ef-ff17-72f3-b814-5a19c146c4d8" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_01a063ef-ff17-72f3-b814-5a19c146c4d8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a063ef-ff17-7338-87e4-ab64907ea065" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_LongTermDebt_01a063ef-ff17-7338-87e4-ab64907ea065" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a063ef-ff17-7fcf-95e7-3487f7e5a768" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a063ef-ff17-7fcf-95e7-3487f7e5a768" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a063ef-ff17-7f29-924e-e9c12c5efc94" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a063ef-ff17-7f29-924e-e9c12c5efc94" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UncommittedAccordionFeature_01a063ef-ff17-7174-a600-100eefaa3035" xlink:href="dpl-20260930.xsd#dpl_UncommittedAccordionFeature"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_dpl_UncommittedAccordionFeature_01a063ef-ff17-7174-a600-100eefaa3035" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_01a063ef-ff17-7567-a2d4-4367ef00ab11" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_LongTermDebtCurrent_01a063ef-ff17-7567-a2d4-4367ef00ab11" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-ff17-7031-94a5-c10340fb048b" 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_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-ff17-7031-94a5-c10340fb048b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_01a063ef-ff17-710d-919d-fc176a60b596" xlink:href="dpl-20260930.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-71bb-bd5d-5cc5f46e27a8" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_01a063ef-ff17-710d-919d-fc176a60b596" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtLongtermDebtDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" 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_01a063ef-ff17-7907-87bf-9da6d36fd1e8" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_DebtInstrumentTable_01a063ef-ff17-7907-87bf-9da6d36fd1e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7d2f-89c8-0fcc6952f822" 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_01a063ef-ff17-7907-87bf-9da6d36fd1e8" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7d2f-89c8-0fcc6952f822" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7d2f-89c8-0fcc6952f822_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_01a063ef-ff17-7d2f-89c8-0fcc6952f822" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7d2f-89c8-0fcc6952f822_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" 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_01a063ef-ff17-7d2f-89c8-0fcc6952f822" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_01a063ef-ff17-70e7-b948-42470abfe686" xlink:href="dpl-20260930.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_01a063ef-ff17-70e7-b948-42470abfe686" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_01a063ef-ff17-79bf-b37f-184dc4e056b8" xlink:href="dpl-20260930.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_01a063ef-ff17-79bf-b37f-184dc4e056b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_01a063ef-ff17-77c6-9300-a1bcd24b40d0" xlink:href="dpl-20260930.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_01a063ef-ff17-77c6-9300-a1bcd24b40d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-7ee4-9629-bc76b677432a" xlink:href="dpl-20260930.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-7ee4-9629-bc76b677432a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-70d1-b64e-09e1830c72a2" xlink:href="dpl-20260930.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_01a063ef-ff17-70d1-b64e-09e1830c72a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_01a063ef-ff17-7926-9b6c-f0ca172e83a5" xlink:href="dpl-20260930.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_01a063ef-ff17-7926-9b6c-f0ca172e83a5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70SeniorNotesDue2033Member_01a063ef-ff17-75b2-9a25-35b7df8965a9" xlink:href="dpl-20260930.xsd#dpl_A5.70SeniorNotesDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A5.70SeniorNotesDue2033Member_01a063ef-ff17-75b2-9a25-35b7df8965a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49SeniorNotesDue2028Member_01a063ef-ff17-7e41-bc50-ce1a0caf9451" xlink:href="dpl-20260930.xsd#dpl_A5.49SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A5.49SeniorNotesDue2028Member_01a063ef-ff17-7e41-bc50-ce1a0caf9451" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_01a063ef-ff17-7309-929a-d194c99f0b8a" xlink:href="dpl-20260930.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_01a063ef-ff17-7309-929a-d194c99f0b8a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49FirstMortgageBondsDue2028Member_01a063ef-ff17-72fb-bd66-ca370a5f65b5" xlink:href="dpl-20260930.xsd#dpl_A5.49FirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7edb-9a53-891ada9aab2c" xlink:to="loc_dpl_A5.49FirstMortgageBondsDue2028Member_01a063ef-ff17-72fb-bd66-ca370a5f65b5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_01a063ef-ff17-75c6-9e33-6ef2c3b4cfd5" xlink:href="dpl-20260930.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_01a063ef-ff17-75c6-9e33-6ef2c3b4cfd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_01a063ef-ff17-73a0-8437-6ef3bcf9584f" xlink:href="dpl-20260930.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_01a063ef-ff17-73a0-8437-6ef3bcf9584f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a063ef-ff17-70d1-a49e-210fc9ebe6e8" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_LongTermDebt_01a063ef-ff17-70d1-a49e-210fc9ebe6e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-ff17-7591-88ab-86c274d92236" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a063ef-ff17-7591-88ab-86c274d92236" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a063ef-ff17-744b-b8e1-a34856d38229" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a063ef-ff17-744b-b8e1-a34856d38229" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a063ef-ff17-7592-bd9e-637b4a1d3a39" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a063ef-ff17-7592-bd9e-637b4a1d3a39" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a063ef-ff17-76d4-9332-de3366d457ef" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_LineOfCredit_01a063ef-ff17-76d4-9332-de3366d457ef" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-ff17-7698-8fef-b14f9a397e1b" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_01a063ef-ff17-7698-8fef-b14f9a397e1b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a063ef-ff17-7f2f-81b8-1b955c9298f8" 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_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a063ef-ff17-7f2f-81b8-1b955c9298f8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_01a063ef-ff17-78b7-9c9d-c1bd08551b7d" xlink:href="dpl-20260930.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a063ef-ff17-7f89-9fed-2ab0dd8a4535" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_01a063ef-ff17-78b7-9c9d-c1bd08551b7d" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7075-a193-8e67c0d75b01" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_01a063ef-ff17-71bf-bb59-e03a2b492bd3" 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_01a063ef-ff17-7075-a193-8e67c0d75b01" xlink:to="loc_dei_EntitiesTable_01a063ef-ff17-71bf-bb59-e03a2b492bd3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-746d-badb-54d20de9f5bf" 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_01a063ef-ff17-71bf-bb59-e03a2b492bd3" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-746d-badb-54d20de9f5bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-746d-badb-54d20de9f5bf_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_01a063ef-ff17-746d-badb-54d20de9f5bf" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-746d-badb-54d20de9f5bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d66-a37b-ef82877c82b3" 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_01a063ef-ff17-746d-badb-54d20de9f5bf" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7d66-a37b-ef82877c82b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7e80-aa86-f3d30c5e7f89" 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_01a063ef-ff17-7d66-a37b-ef82877c82b3" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7e80-aa86-f3d30c5e7f89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-7469-bf69-79dc78c2e72c" 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_01a063ef-ff17-7075-a193-8e67c0d75b01" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-7469-bf69-79dc78c2e72c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-7b31-b4e7-a1edbfe82d1f" xlink:href="dpl-20260930.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_01a063ef-ff17-7075-a193-8e67c0d75b01" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-7b31-b4e7-a1edbfe82d1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_01a063ef-ff17-742d-b172-b2a41ed378c7" 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_01a063ef-ff17-7075-a193-8e67c0d75b01" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_01a063ef-ff17-742d-b172-b2a41ed378c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_01a063ef-ff17-7cc9-b7fd-fb8ab31565a5" 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_01a063ef-ff17-7574-8bf9-e390868d5d0c" 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_01a063ef-ff17-7cc9-b7fd-fb8ab31565a5" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_01a063ef-ff17-7574-8bf9-e390868d5d0c" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-727a-8409-c7e3ada181b7" xlink:href="dpl-20260930.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_01a063ef-ff17-7cc9-b7fd-fb8ab31565a5" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_01a063ef-ff17-727a-8409-c7e3ada181b7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansNetPeriodicBenefitCostIncomeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-785f-942c-d61df3ff2c41" 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_01a063ef-ff17-795a-99c0-2381db644243" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_01a063ef-ff17-795a-99c0-2381db644243" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7f29-bb34-928719808932" 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_01a063ef-ff17-795a-99c0-2381db644243" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7f29-bb34-928719808932" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7f29-bb34-928719808932_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_01a063ef-ff17-7f29-bb34-928719808932" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7f29-bb34-928719808932_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7c19-858e-579c42d68a05" 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_01a063ef-ff17-7f29-bb34-928719808932" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7c19-858e-579c42d68a05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7605-9c76-d05018db291e" 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_01a063ef-ff17-7c19-858e-579c42d68a05" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7605-9c76-d05018db291e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_01a063ef-ff17-776c-873d-0603e500746c" 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_01a063ef-ff17-795a-99c0-2381db644243" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_01a063ef-ff17-776c-873d-0603e500746c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-776c-873d-0603e500746c_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_01a063ef-ff17-776c-873d-0603e500746c" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-776c-873d-0603e500746c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7c26-9756-30067e4d9231" 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_01a063ef-ff17-776c-873d-0603e500746c" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_01a063ef-ff17-7c26-9756-30067e4d9231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_01a063ef-ff17-7c19-bdf4-c2c1ba7fe6c7" 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_01a063ef-ff17-7c26-9756-30067e4d9231" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_01a063ef-ff17-7c19-bdf4-c2c1ba7fe6c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_01a063ef-ff17-73dd-a403-b8b741d12b19" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_01a063ef-ff17-73dd-a403-b8b741d12b19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_01a063ef-ff17-78b9-b181-3239c51494c5" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_01a063ef-ff17-78b9-b181-3239c51494c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_01a063ef-ff17-7749-840a-7688d21e71ed" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_01a063ef-ff17-7749-840a-7688d21e71ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_01a063ef-ff17-75df-8bea-d742e77102bd" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_01a063ef-ff17-75df-8bea-d742e77102bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_01a063ef-ff17-7d53-9572-577da21e4944" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_01a063ef-ff17-7d53-9572-577da21e4944" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_01a063ef-ff17-748f-86b7-09ba69147085" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_01a063ef-ff17-748f-86b7-09ba69147085" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_01a063ef-ff17-7964-b1ea-e47532addd50" 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_01a063ef-ff17-785f-942c-d61df3ff2c41" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_01a063ef-ff17-7964-b1ea-e47532addd50" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/EquityDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-705b-a652-f9e2add55579" 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_dpl_EquityTable_01a063ef-ff17-78cc-94cd-73c1b9e59e62" xlink:href="dpl-20260930.xsd#dpl_EquityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_dpl_EquityTable_01a063ef-ff17-78cc-94cd-73c1b9e59e62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7bc3-9ad6-16a75cc748bc" 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_EquityTable_01a063ef-ff17-78cc-94cd-73c1b9e59e62" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7bc3-9ad6-16a75cc748bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7bc3-9ad6-16a75cc748bc_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_01a063ef-ff17-7bc3-9ad6-16a75cc748bc" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7bc3-9ad6-16a75cc748bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-72af-bfbf-1983081ce442" 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_01a063ef-ff17-7bc3-9ad6-16a75cc748bc" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-72af-bfbf-1983081ce442" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-72af-952d-a802e64d633d" 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_01a063ef-ff17-72af-bfbf-1983081ce442" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-72af-952d-a802e64d633d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-ff17-7567-abb7-53e6fa232d99" 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_EquityTable_01a063ef-ff17-78cc-94cd-73c1b9e59e62" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a063ef-ff17-7567-abb7-53e6fa232d99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-ff17-7567-abb7-53e6fa232d99_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_01a063ef-ff17-7567-abb7-53e6fa232d99" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-ff17-7567-abb7-53e6fa232d99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a063ef-ff17-7ce4-809a-07c8e8bc99d5" 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_01a063ef-ff17-7567-abb7-53e6fa232d99" xlink:to="loc_us-gaap_EquityComponentDomain_01a063ef-ff17-7ce4-809a-07c8e8bc99d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_01a063ef-ff17-72ab-a6b6-3cee95094fc4" 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_01a063ef-ff17-7ce4-809a-07c8e8bc99d5" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_01a063ef-ff17-72ab-a6b6-3cee95094fc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_01a063ef-ff17-77a2-910d-7afcf347a6ae" 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_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_01a063ef-ff17-77a2-910d-7afcf347a6ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-ff17-7e7c-b12b-e7e105ab6b9a" 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_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_01a063ef-ff17-7e7c-b12b-e7e105ab6b9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_01a063ef-ff17-74f8-a385-e9a0675c0d6a" 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_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_us-gaap_StockholdersEquityOther_01a063ef-ff17-74f8-a385-e9a0675c0d6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-ff17-738e-ac66-347821dc5254" 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_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a063ef-ff17-738e-ac66-347821dc5254" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-ff17-7cc9-9fe9-58b1b3000cd8" 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_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_01a063ef-ff17-7cc9-9fe9-58b1b3000cd8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentPercent_01a063ef-ff17-757e-ac09-cfca79d1309e" xlink:href="dpl-20260930.xsd#dpl_CDPQInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_dpl_CDPQInvestmentPercent_01a063ef-ff17-757e-ac09-cfca79d1309e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsInvestmentPercent_01a063ef-ff17-793e-96f5-30f74f9e94a2" xlink:href="dpl-20260930.xsd#dpl_OhioHoldingsInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-705b-a652-f9e2add55579" xlink:to="loc_dpl_OhioHoldingsInvestmentPercent_01a063ef-ff17-793e-96f5-30f74f9e94a2" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7de2-aaab-469acc79a71e" 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_01a063ef-ff17-7bac-8919-887719b100ee" 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_01a063ef-ff17-7de2-aaab-469acc79a71e" xlink:to="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_01a063ef-ff17-7bac-8919-887719b100ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c" 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_01a063ef-ff17-7bac-8919-887719b100ee" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c_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_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a063ef-ff17-79b6-aa95-5250a047b7bc" 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_01a063ef-ff17-73c6-b3fc-d7d6ec683d3c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a063ef-ff17-79b6-aa95-5250a047b7bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricGenerationCompanyMember_01a063ef-ff17-786d-a21d-89670c3f9274" xlink:href="dpl-20260930.xsd#dpl_ElectricGenerationCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a063ef-ff17-79b6-aa95-5250a047b7bc" xlink:to="loc_dpl_ElectricGenerationCompanyMember_01a063ef-ff17-786d-a21d-89670c3f9274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7040-a10d-3c8ae2ffaa28" 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_01a063ef-ff17-7bac-8919-887719b100ee" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a063ef-ff17-7040-a10d-3c8ae2ffaa28" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7040-a10d-3c8ae2ffaa28_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_01a063ef-ff17-7040-a10d-3c8ae2ffaa28" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7040-a10d-3c8ae2ffaa28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7dd9-a7c8-f053c227460b" 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_01a063ef-ff17-7040-a10d-3c8ae2ffaa28" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7dd9-a7c8-f053c227460b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtObligationOn49EquityOwnershipMember_01a063ef-ff17-7b25-af9a-76dc1aa12344" xlink:href="dpl-20260930.xsd#dpl_DebtObligationOn49EquityOwnershipMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a063ef-ff17-7dd9-a7c8-f053c227460b" xlink:to="loc_dpl_DebtObligationOn49EquityOwnershipMember_01a063ef-ff17-7b25-af9a-76dc1aa12344" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7803-91ac-9f2862948549" 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_01a063ef-ff17-7bac-8919-887719b100ee" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7803-91ac-9f2862948549" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7803-91ac-9f2862948549_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_01a063ef-ff17-7803-91ac-9f2862948549" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7803-91ac-9f2862948549_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-715c-ac07-21be2260577c" 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_01a063ef-ff17-7803-91ac-9f2862948549" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-715c-ac07-21be2260577c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7f83-931e-3396f9cba412" 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_01a063ef-ff17-715c-ac07-21be2260577c" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7f83-931e-3396f9cba412" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_01a063ef-ff17-7089-baff-0ebf66b2a5b9" xlink:href="dpl-20260930.xsd#dpl_PublicUtilitiesEquityInterestCostMethodPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_01a063ef-ff17-7de2-aaab-469acc79a71e" xlink:to="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_01a063ef-ff17-7089-baff-0ebf66b2a5b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_01a063ef-ff17-7392-b893-5fee6c826628" xlink:href="dpl-20260930.xsd#dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_01a063ef-ff17-7de2-aaab-469acc79a71e" xlink:to="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_01a063ef-ff17-7392-b893-5fee6c826628" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_01a063ef-ff17-7a0e-8170-d78b5b014d2d" 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_01a063ef-ff17-7de2-aaab-469acc79a71e" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_01a063ef-ff17-7a0e-8170-d78b5b014d2d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" 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_01a063ef-ff17-74a6-9ef3-682ca669c3a5" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a063ef-ff17-74a6-9ef3-682ca669c3a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7f6f-9b82-522e999e3d6b" 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_01a063ef-ff17-74a6-9ef3-682ca669c3a5" xlink:to="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7f6f-9b82-522e999e3d6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7f6f-9b82-522e999e3d6b_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_01a063ef-ff17-7f6f-9b82-522e999e3d6b" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7f6f-9b82-522e999e3d6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7748-b9e6-c3742d0b9b19" 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_01a063ef-ff17-7f6f-9b82-522e999e3d6b" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7748-b9e6-c3742d0b9b19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a063ef-ff17-7d7c-a469-64a717bb43ca" 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_01a063ef-ff17-7748-b9e6-c3742d0b9b19" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a063ef-ff17-7d7c-a469-64a717bb43ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7ff1-b5de-0adca4f16def" 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_01a063ef-ff17-74a6-9ef3-682ca669c3a5" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7ff1-b5de-0adca4f16def" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7ff1-b5de-0adca4f16def_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_01a063ef-ff17-7ff1-b5de-0adca4f16def" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7ff1-b5de-0adca4f16def_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7668-887a-de0d1259a8f3" 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_01a063ef-ff17-7ff1-b5de-0adca4f16def" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7668-887a-de0d1259a8f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_01a063ef-ff17-7bd4-ac3e-0ddbbb529a47" xlink:href="dpl-20260930.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a063ef-ff17-7668-887a-de0d1259a8f3" xlink:to="loc_dpl_UtilityMember_01a063ef-ff17-7bd4-ac3e-0ddbbb529a47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ab7-9719-bc385c55c3b2" 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_01a063ef-ff17-74a6-9ef3-682ca669c3a5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7ab7-9719-bc385c55c3b2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ab7-9719-bc385c55c3b2_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_01a063ef-ff17-7ab7-9719-bc385c55c3b2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7ab7-9719-bc385c55c3b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7abc-8039-c9eebcbe73a6" 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_01a063ef-ff17-7ab7-9719-bc385c55c3b2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7abc-8039-c9eebcbe73a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7ad4-b2fe-9aa29cbbed10" 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_01a063ef-ff17-7abc-8039-c9eebcbe73a6" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7ad4-b2fe-9aa29cbbed10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a063ef-ff17-742f-baa9-d7cebdcb50a1" 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_01a063ef-ff17-74a6-9ef3-682ca669c3a5" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a063ef-ff17-742f-baa9-d7cebdcb50a1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-742f-baa9-d7cebdcb50a1_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_01a063ef-ff17-742f-baa9-d7cebdcb50a1" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-742f-baa9-d7cebdcb50a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-7dee-82e6-903b6786cb85" 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_01a063ef-ff17-742f-baa9-d7cebdcb50a1" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-7dee-82e6-903b6786cb85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a063ef-ff17-74fd-9432-5cb6acd7bdf1" 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_01a063ef-ff17-7dee-82e6-903b6786cb85" xlink:to="loc_us-gaap_RelatedPartyMember_01a063ef-ff17-74fd-9432-5cb6acd7bdf1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_01a063ef-ff17-76bd-81d8-fcc0c1ece3cf" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_NumberOfOperatingSegments_01a063ef-ff17-76bd-81d8-fcc0c1ece3cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_01a063ef-ff17-7d96-bd8a-e4d014fca36e" xlink:href="dpl-20260930.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_dpl_NumberOfRetailCustomers_01a063ef-ff17-7d96-bd8a-e4d014fca36e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_01a063ef-ff17-71f5-9dc0-d407fc210e17" xlink:href="dpl-20260930.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_dpl_ServiceAreaSquareMiles_01a063ef-ff17-71f5-9dc0-d407fc210e17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a063ef-ff17-7136-9b51-dd9d5f7a6165" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_Assets_01a063ef-ff17-7136-9b51-dd9d5f7a6165" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a063ef-ff17-75d0-9232-f5a9b0051e58" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_Revenues_01a063ef-ff17-75d0-9232-f5a9b0051e58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-ff17-7bca-9da9-04aa67fcd305" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-ff17-7bca-9da9-04aa67fcd305" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-ff17-7ef0-86be-6de354546733" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-ff17-7ef0-86be-6de354546733" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-ff17-7a7d-92ac-6832bdb8d91f" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-ff17-7a7d-92ac-6832bdb8d91f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-ff17-716f-8cf4-ac23a63e12d9" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-ff17-716f-8cf4-ac23a63e12d9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_01a063ef-ff17-7cca-b053-31890b054f11" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_InterestAndDebtExpense_01a063ef-ff17-7cca-b053-31890b054f11" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_01a063ef-ff17-794c-a87b-6f738e66505c" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_01a063ef-ff17-794c-a87b-6f738e66505c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-ff17-7512-aeca-61456880cf2c" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-ff17-7512-aeca-61456880cf2c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-ff17-7921-864e-fc3aee8a9c67" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-ff17-7921-864e-fc3aee8a9c67" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-ff17-7243-8b41-db46fd75c708" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-ff17-7243-8b41-db46fd75c708" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a063ef-ff17-7ebc-a79b-7bd65e0b790a" 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_01a063ef-ff17-7f77-be5a-f67f2eb8c21f" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a063ef-ff17-7ebc-a79b-7bd65e0b790a" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsSegmentFinancialInformationDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-74df-a590-7857629c134e" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff_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_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7d7b-b93c-6a950332558a" 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_01a063ef-ff17-7eeb-9ab1-f6d5c5834bff" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7d7b-b93c-6a950332558a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7dee-837c-d62d7dc95e3f" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7dee-837c-d62d7dc95e3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7dee-837c-d62d7dc95e3f_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_01a063ef-ff17-7dee-837c-d62d7dc95e3f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7dee-837c-d62d7dc95e3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-795c-81d3-85953427fceb" 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_01a063ef-ff17-7dee-837c-d62d7dc95e3f" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-795c-81d3-85953427fceb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-701f-9733-a980e23ae100" 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_01a063ef-ff17-795c-81d3-85953427fceb" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-701f-9733-a980e23ae100" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7935-a0f9-bd17abc5c21c" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:to="loc_srt_ConsolidationItemsAxis_01a063ef-ff17-7935-a0f9-bd17abc5c21c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7935-a0f9-bd17abc5c21c_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_01a063ef-ff17-7935-a0f9-bd17abc5c21c" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7935-a0f9-bd17abc5c21c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7890-b453-a66956ba2a80" 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_01a063ef-ff17-7935-a0f9-bd17abc5c21c" xlink:to="loc_srt_ConsolidationItemsDomain_01a063ef-ff17-7890-b453-a66956ba2a80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a063ef-ff17-7514-8f08-de91f248beb6" 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_01a063ef-ff17-7890-b453-a66956ba2a80" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a063ef-ff17-7514-8f08-de91f248beb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7477-afe8-544c1ff259c7" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7477-afe8-544c1ff259c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7477-afe8-544c1ff259c7_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_01a063ef-ff17-7477-afe8-544c1ff259c7" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7477-afe8-544c1ff259c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7fba-a517-a38e82732c9f" 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_01a063ef-ff17-7477-afe8-544c1ff259c7" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7fba-a517-a38e82732c9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_01a063ef-ff17-784b-aec9-8f8d1b5eab6d" xlink:href="dpl-20260930.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a063ef-ff17-7fba-a517-a38e82732c9f" xlink:to="loc_dpl_UtilityMember_01a063ef-ff17-784b-aec9-8f8d1b5eab6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a063ef-ff17-7305-9898-68a92c8cd9b7" 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_01a063ef-ff17-747a-a96b-ef9a9f89033d" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a063ef-ff17-7305-9898-68a92c8cd9b7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-7305-9898-68a92c8cd9b7_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_01a063ef-ff17-7305-9898-68a92c8cd9b7" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-7305-9898-68a92c8cd9b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-76a3-b3cf-d48430ff6116" 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_01a063ef-ff17-7305-9898-68a92c8cd9b7" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a063ef-ff17-76a3-b3cf-d48430ff6116" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a063ef-ff17-7672-b5fa-b4bbb59e4a73" 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_01a063ef-ff17-76a3-b3cf-d48430ff6116" xlink:to="loc_us-gaap_RelatedPartyMember_01a063ef-ff17-7672-b5fa-b4bbb59e4a73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a063ef-ff17-786a-906c-c70ad99c5707" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_Revenues_01a063ef-ff17-786a-906c-c70ad99c5707" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-ff17-7e4c-9bee-3be411759fd6" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_01a063ef-ff17-7e4c-9bee-3be411759fd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_01a063ef-ff17-7b7d-923c-f70d244156e0" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_InterestAndDebtExpense_01a063ef-ff17-7b7d-923c-f70d244156e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a063ef-ff17-7609-a07c-bf1f5f8022ae" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_Assets_01a063ef-ff17-7609-a07c-bf1f5f8022ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-ff17-7874-b762-0469891bdaae" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a063ef-ff17-7874-b762-0469891bdaae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-ff17-7be8-b2b5-cc595da81b7b" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_01a063ef-ff17-7be8-b2b5-cc595da81b7b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-ff17-72b2-8b51-e21b4a31c21e" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_01a063ef-ff17-72b2-8b51-e21b4a31c21e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-ff17-7510-a35d-469accee311a" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_01a063ef-ff17-7510-a35d-469accee311a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_01a063ef-ff17-736f-8ee9-736c72f4ff5c" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_01a063ef-ff17-736f-8ee9-736c72f4ff5c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-ff17-788f-8e92-60b70110f56b" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a063ef-ff17-788f-8e92-60b70110f56b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a063ef-ff17-7d3e-bcb1-8c64ecb334fc" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_NetIncomeLoss_01a063ef-ff17-7d3e-bcb1-8c64ecb334fc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_01a063ef-ff17-7c27-80e4-1f9615f253de" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_01a063ef-ff17-7c27-80e4-1f9615f253de" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a063ef-ff17-7a6e-9411-54fc25dc478e" 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_01a063ef-ff17-74df-a590-7857629c134e" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_01a063ef-ff17-7a6e-9411-54fc25dc478e" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" 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_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a063ef-ff17-78d5-8e5a-e560ead5afc4" 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_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:to="loc_srt_ProductOrServiceAxis_01a063ef-ff17-78d5-8e5a-e560ead5afc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-78d5-8e5a-e560ead5afc4_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_01a063ef-ff17-78d5-8e5a-e560ead5afc4" xlink:to="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-78d5-8e5a-e560ead5afc4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-7ac6-8e85-9b3cad2fb60e" 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_01a063ef-ff17-78d5-8e5a-e560ead5afc4" xlink:to="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-7ac6-8e85-9b3cad2fb60e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_01a063ef-ff17-740b-ac33-51a15c8297e1" xlink:href="dpl-20260930.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-7ac6-8e85-9b3cad2fb60e" xlink:to="loc_dpl_OtherRevenuesMember_01a063ef-ff17-740b-ac33-51a15c8297e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_WholesaleRevenueMember_01a063ef-ff17-7b24-bb87-2c57dee46f4d" xlink:href="dpl-20260930.xsd#dpl_WholesaleRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-7ac6-8e85-9b3cad2fb60e" xlink:to="loc_dpl_WholesaleRevenueMember_01a063ef-ff17-7b24-bb87-2c57dee46f4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RetailRevenueMember_01a063ef-ff17-7028-81f2-84ca5065ed77" xlink:href="dpl-20260930.xsd#dpl_RetailRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a063ef-ff17-7ac6-8e85-9b3cad2fb60e" xlink:to="loc_dpl_RetailRevenueMember_01a063ef-ff17-7028-81f2-84ca5065ed77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7e7a-878b-3263bfd0a0eb" 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_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a063ef-ff17-7e7a-878b-3263bfd0a0eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7e7a-878b-3263bfd0a0eb_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_01a063ef-ff17-7e7a-878b-3263bfd0a0eb" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7e7a-878b-3263bfd0a0eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a063ef-ff17-7cd9-aa9c-afb9fc21da01" 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_01a063ef-ff17-7e7a-878b-3263bfd0a0eb" xlink:to="loc_us-gaap_SegmentDomain_01a063ef-ff17-7cd9-aa9c-afb9fc21da01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_01a063ef-ff17-791f-908b-6cc39dc45054" xlink:href="dpl-20260930.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a063ef-ff17-7cd9-aa9c-afb9fc21da01" xlink:to="loc_dpl_UtilityMember_01a063ef-ff17-791f-908b-6cc39dc45054" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_01a063ef-ff17-7429-a8f0-ccbb8dfaa045" xlink:href="dpl-20260930.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:to="loc_dpl_RevenueTypeAxis_01a063ef-ff17-7429-a8f0-ccbb8dfaa045" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7429-a8f0-ccbb8dfaa045_default" xlink:href="dpl-20260930.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_01a063ef-ff17-7429-a8f0-ccbb8dfaa045" xlink:to="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7429-a8f0-ccbb8dfaa045_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:href="dpl-20260930.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_01a063ef-ff17-7429-a8f0-ccbb8dfaa045" xlink:to="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ResidentialRevenueMember_01a063ef-ff17-7c32-bc16-ea639af77148" xlink:href="dpl-20260930.xsd#dpl_ResidentialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:to="loc_dpl_ResidentialRevenueMember_01a063ef-ff17-7c32-bc16-ea639af77148" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CommercialRevenueMember_01a063ef-ff17-7b85-8eb4-1da8cdb5c229" xlink:href="dpl-20260930.xsd#dpl_CommercialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:to="loc_dpl_CommercialRevenueMember_01a063ef-ff17-7b85-8eb4-1da8cdb5c229" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IndustrialRevenueMember_01a063ef-ff17-7eee-8348-046dd92dbf58" xlink:href="dpl-20260930.xsd#dpl_IndustrialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:to="loc_dpl_IndustrialRevenueMember_01a063ef-ff17-7eee-8348-046dd92dbf58" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_GovernmentalRevenueMember_01a063ef-ff17-7b31-b27f-d3183ca53380" xlink:href="dpl-20260930.xsd#dpl_GovernmentalRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:to="loc_dpl_GovernmentalRevenueMember_01a063ef-ff17-7b31-b27f-d3183ca53380" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_01a063ef-ff17-7a41-b9c4-e7c69aa399d3" xlink:href="dpl-20260930.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_01a063ef-ff17-7714-bb32-51e9301306c9" xlink:to="loc_dpl_OtherRevenuesMember_01a063ef-ff17-7a41-b9c4-e7c69aa399d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7fb1-821c-f6e1604d07a7" 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_DisaggregationOfRevenueTable_01a063ef-ff17-76c1-a5dc-7a7db946d49e" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7fb1-821c-f6e1604d07a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7fb1-821c-f6e1604d07a7_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_01a063ef-ff17-7fb1-821c-f6e1604d07a7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7fb1-821c-f6e1604d07a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7604-babb-5a966fcfb16a" 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_01a063ef-ff17-7fb1-821c-f6e1604d07a7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7604-babb-5a966fcfb16a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-7668-8c1a-f7ca8c1c1d16" 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_01a063ef-ff17-7604-babb-5a966fcfb16a" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-7668-8c1a-f7ca8c1c1d16" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a063ef-ff17-7f77-9abd-86743839c3b5" 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_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a063ef-ff17-7f77-9abd-86743839c3b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Othernon606revenue_01a063ef-ff17-7a51-950c-88238261b34a" xlink:href="dpl-20260930.xsd#dpl_Othernon606revenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_dpl_Othernon606revenue_01a063ef-ff17-7a51-950c-88238261b34a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTORevenue_01a063ef-ff17-70e0-abc1-25dbf33c3147" xlink:href="dpl-20260930.xsd#dpl_RTORevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_dpl_RTORevenue_01a063ef-ff17-70e0-abc1-25dbf33c3147" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTOCapacityRevenue_01a063ef-ff17-782b-8b27-5016fba729e9" xlink:href="dpl-20260930.xsd#dpl_RTOCapacityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_dpl_RTOCapacityRevenue_01a063ef-ff17-782b-8b27-5016fba729e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a063ef-ff17-718b-9ca4-9223431252c4" 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_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_us-gaap_Revenues_01a063ef-ff17-718b-9ca4-9223431252c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_01a063ef-ff17-7b2c-bf9d-343d39d5fff8" 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_01a063ef-ff17-79fb-9e1b-f8abe5baf5b6" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_01a063ef-ff17-7b2c-bf9d-343d39d5fff8" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsDetails" xlink:type="simple" xlink:href="dpl-20260930.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_01a063ef-ff17-7fd1-af66-2d0541cce3f6" 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_01a063ef-ff17-7f85-b09f-f69dc5ccb075" 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_01a063ef-ff17-7fd1-af66-2d0541cce3f6" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a063ef-ff17-7f85-b09f-f69dc5ccb075" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7669-a2b7-02810d2ccb69" 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_01a063ef-ff17-7f85-b09f-f69dc5ccb075" xlink:to="loc_srt_ConsolidatedEntitiesAxis_01a063ef-ff17-7669-a2b7-02810d2ccb69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7669-a2b7-02810d2ccb69_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_01a063ef-ff17-7669-a2b7-02810d2ccb69" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-7669-a2b7-02810d2ccb69_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-739b-9407-baa10fae0ce6" 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_01a063ef-ff17-7669-a2b7-02810d2ccb69" xlink:to="loc_srt_ConsolidatedEntitiesDomain_01a063ef-ff17-739b-9407-baa10fae0ce6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_01a063ef-ff17-786b-9021-8c857ece26af" 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_01a063ef-ff17-739b-9407-baa10fae0ce6" xlink:to="loc_srt_SubsidiariesMember_01a063ef-ff17-786b-9021-8c857ece26af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a063ef-ff17-7237-b758-47b2a4fab4ed" 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_01a063ef-ff17-7f85-b09f-f69dc5ccb075" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_01a063ef-ff17-7237-b758-47b2a4fab4ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7237-b758-47b2a4fab4ed_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_01a063ef-ff17-7237-b758-47b2a4fab4ed" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7237-b758-47b2a4fab4ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7db6-8a2d-80075504e62b" 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_01a063ef-ff17-7237-b758-47b2a4fab4ed" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_01a063ef-ff17-7db6-8a2d-80075504e62b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-789f-b7ed-429796274371" 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_01a063ef-ff17-7f85-b09f-f69dc5ccb075" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a063ef-ff17-789f-b7ed-429796274371" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-789f-b7ed-429796274371_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_01a063ef-ff17-789f-b7ed-429796274371" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-789f-b7ed-429796274371_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e42-bd4d-31414b9563df" 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_01a063ef-ff17-789f-b7ed-429796274371" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a063ef-ff17-7e42-bd4d-31414b9563df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_01a063ef-ff17-768b-a114-534fb263347b" 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_01a063ef-ff17-7fd1-af66-2d0541cce3f6" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_01a063ef-ff17-768b-a114-534fb263347b" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
