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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019dd587-6f2a-7bd0-9101-d38bbf07fdda,g:35b97bd6-a714-482c-b5d2-fdf4e6120cec-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.dpandl.com/role/CoverStatement" xlink:type="simple" xlink:href="dpl-20260331.xsd#CoverStatement"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CoverStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7097-7b9f-9d25-2f6e99b87b31" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntitiesTable_019dd587-7097-7b9f-9d25-2f6e99b87b31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-70b7-ba8d-74af87bced01" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7097-7b9f-9d25-2f6e99b87b31" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-70b7-ba8d-74af87bced01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-70b7-ba8d-74af87bced01_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-70b7-ba8d-74af87bced01" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-70b7-ba8d-74af87bced01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7779-bb28-02ef0518c115" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-70b7-ba8d-74af87bced01" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7779-bb28-02ef0518c115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-7cc6-a403-d85b62021784" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7779-bb28-02ef0518c115" xlink:to="loc_srt_SubsidiariesMember_019dd587-7097-7cc6-a403-d85b62021784" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019dd587-7097-717b-8228-365d28acbf4d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentFiscalYearFocus_019dd587-7097-717b-8228-365d28acbf4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019dd587-7097-7f17-8623-ed31d0475774" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019dd587-7097-7f17-8623-ed31d0475774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019dd587-7097-72d3-a905-ffbe164acf3c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityCentralIndexKey_019dd587-7097-72d3-a905-ffbe164acf3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019dd587-7097-720f-8347-9d00eeea092a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_CurrentFiscalYearEndDate_019dd587-7097-720f-8347-9d00eeea092a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019dd587-7097-7f6a-8952-b07932286631" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_AmendmentFlag_019dd587-7097-7f6a-8952-b07932286631" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019dd587-7097-7226-ac23-caa791cbed58" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityCurrentReportingStatus_019dd587-7097-7226-ac23-caa791cbed58" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019dd587-7097-7561-92c3-0fffdf1c8999" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentType_019dd587-7097-7561-92c3-0fffdf1c8999" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019dd587-7097-7116-bcf8-173962d29860" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentQuarterlyReport_019dd587-7097-7116-bcf8-173962d29860" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019dd587-7097-71c9-bb16-893fe5bb65e4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityInteractiveDataCurrent_019dd587-7097-71c9-bb16-893fe5bb65e4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019dd587-7097-7cfb-9465-d996690c0cc6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityFilerCategory_019dd587-7097-7cfb-9465-d996690c0cc6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019dd587-7097-74c0-897f-d07fcb8e6bba" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityShellCompany_019dd587-7097-74c0-897f-d07fcb8e6bba" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019dd587-7097-7fc9-95b4-d6241d79f622" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentPeriodEndDate_019dd587-7097-7fc9-95b4-d6241d79f622" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019dd587-7097-7d21-95e3-4d19bea70c0c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_DocumentTransitionReport_019dd587-7097-7d21-95e3-4d19bea70c0c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019dd587-7097-7487-ac43-0f9cfa0372c4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityRegistrantName_019dd587-7097-7487-ac43-0f9cfa0372c4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019dd587-7097-7e95-8390-1c84c7640992" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019dd587-7097-7e95-8390-1c84c7640992" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019dd587-7097-7938-af91-5267d73e33bb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityFileNumber_019dd587-7097-7938-af91-5267d73e33bb" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019dd587-7097-7c26-8c11-5d7fb9a53bf3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityAddressAddressLine1_019dd587-7097-7c26-8c11-5d7fb9a53bf3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019dd587-7097-7906-9995-bfcaab3a30bf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityAddressPostalZipCode_019dd587-7097-7906-9995-bfcaab3a30bf" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019dd587-7097-7972-a18e-01a53039cb72" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_LocalPhoneNumber_019dd587-7097-7972-a18e-01a53039cb72" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019dd587-7097-7c17-bd26-8510d0852f19" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityTaxIdentificationNumber_019dd587-7097-7c17-bd26-8510d0852f19" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019dd587-7097-75a5-8d09-a40507f88c39" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntitySmallBusiness_019dd587-7097-75a5-8d09-a40507f88c39" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019dd587-7097-7661-b2db-8557aa555a3c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityEmergingGrowthCompany_019dd587-7097-7661-b2db-8557aa555a3c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019dd587-7097-7de4-b4d5-c803cfb940cd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019dd587-7097-7de4-b4d5-c803cfb940cd" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019dd587-7097-78f3-b5a1-9a8225b036e9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityAddressCityOrTown_019dd587-7097-78f3-b5a1-9a8225b036e9" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019dd587-7097-7d21-9151-f02778e1d7be" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_EntityAddressStateOrProvince_019dd587-7097-7d21-9151-f02778e1d7be" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019dd587-7097-7330-b503-9b45d51ab725" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7097-7fc5-92a2-0c100c54c0e8" xlink:to="loc_dei_CityAreaCode_019dd587-7097-7330-b503-9b45d51ab725" xlink:type="arc" order="25"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-710e-843c-bbae6bfa69ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-710e-843c-bbae6bfa69ce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-7097-79e4-89d2-dbb7dafe88ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_Revenues_019dd587-7097-79e4-89d2-dbb7dafe88ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-7097-7634-b2b8-949c9b323dd1" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-7097-7634-b2b8-949c9b323dd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-7097-73b0-9f2b-2b5e7657a4b8" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-7097-73b0-9f2b-2b5e7657a4b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019dd587-7097-7ad1-b53f-335ea351ee56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_CostsAndExpenses_019dd587-7097-7ad1-b53f-335ea351ee56" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019dd587-7097-7f0e-b82f-2ba1f9080c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_OperatingIncomeLoss_019dd587-7097-7f0e-b82f-2ba1f9080c0d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-7097-7515-89b8-f593608f9953" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-7097-7515-89b8-f593608f9953" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-7097-789d-b09b-cee45ce27348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-7097-789d-b09b-cee45ce27348" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd5c9-dfda-790f-86a0-b5a644e6c59e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_NetIncomeLoss_019dd5c9-dfda-790f-86a0-b5a644e6c59e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-7097-7ab2-87ae-0e1ff24a5a11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_ProfitLoss_019dd587-7097-7ab2-87ae-0e1ff24a5a11" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_019dd587-7097-7168-abaf-7088a0701038" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_019dd587-7097-7168-abaf-7088a0701038" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-7097-7653-9857-9d3f755d5110" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-7097-7653-9857-9d3f755d5110" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-7097-73e8-8a93-b462dc75db36" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-7097-73e8-8a93-b462dc75db36" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-7097-7370-a384-66f8cf50c2fc" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-7097-7370-a384-66f8cf50c2fc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dd587-7097-7f80-96cd-a428a662b626" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dd587-7097-7f80-96cd-a428a662b626" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-7097-777a-b7af-05d8bd2def8c" 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_019dd587-7097-73f3-9404-7d017fd31696" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-7097-777a-b7af-05d8bd2def8c" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-71f5-b6f1-867f216069c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-71f5-b6f1-867f216069c6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-7d77-aa2b-c705b94af85b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-71f5-b6f1-867f216069c6" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-7d77-aa2b-c705b94af85b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-7d77-aa2b-c705b94af85b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-7d77-aa2b-c705b94af85b" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-7d77-aa2b-c705b94af85b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-745b-881b-679c0edcd09c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-7d77-aa2b-c705b94af85b" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-745b-881b-679c0edcd09c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019dd587-7097-79e1-8870-c430d028f116" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-745b-881b-679c0edcd09c" xlink:to="loc_us-gaap_RetainedEarningsMember_019dd587-7097-79e1-8870-c430d028f116" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7097-73c3-ad27-110f08243299" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-745b-881b-679c0edcd09c" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7097-73c3-ad27-110f08243299" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-7769-8341-ba542ff43414" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-71f5-b6f1-867f216069c6" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-7769-8341-ba542ff43414" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7769-8341-ba542ff43414_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-7769-8341-ba542ff43414" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7769-8341-ba542ff43414_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7470-8162-238ad95aa923" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-7769-8341-ba542ff43414" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7470-8162-238ad95aa923" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-7097-7ac8-97ae-0b7f83ba0887" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7470-8162-238ad95aa923" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-7097-7ac8-97ae-0b7f83ba0887" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7c66-a1dd-ccb0e6469398" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-71f5-b6f1-867f216069c6" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7c66-a1dd-ccb0e6469398" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7c66-a1dd-ccb0e6469398_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7c66-a1dd-ccb0e6469398" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7c66-a1dd-ccb0e6469398_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7b2e-a48d-6e8811a834a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7c66-a1dd-ccb0e6469398" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7b2e-a48d-6e8811a834a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-7097-7954-96a7-eede139f0764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7b2e-a48d-6e8811a834a2" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-7097-7954-96a7-eede139f0764" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-7097-7988-8e5e-e6b7e0ed0907" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:to="loc_us-gaap_ProfitLoss_019dd587-7097-7988-8e5e-e6b7e0ed0907" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-7726-87a9-e1c360337d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-7726-87a9-e1c360337d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-70fa-8fd8-28ae193be7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-7726-87a9-e1c360337d4e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-70fa-8fd8-28ae193be7b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019dd587-7097-74d5-877b-5f86fa9f3bf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-7726-87a9-e1c360337d4e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019dd587-7097-74d5-877b-5f86fa9f3bf4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-738f-bc7b-5e9de2f42ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-738f-bc7b-5e9de2f42ac0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-71b8-abc6-f75c233f8ca9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-738f-bc7b-5e9de2f42ac0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-71b8-abc6-f75c233f8ca9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dd587-7097-7e7d-9b03-2f041504b908" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-738f-bc7b-5e9de2f42ac0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019dd587-7097-7e7d-9b03-2f041504b908" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e34-9ed8-a1ce588669cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_019dd587-7097-738f-bc7b-5e9de2f42ac0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e34-9ed8-a1ce588669cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-79cc-8056-7ba2531bcfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-75b8-841e-8a636770f6f5" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-79cc-8056-7ba2531bcfa1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-7f80-beda-30711d7e0c5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-7f80-beda-30711d7e0c5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-7097-756f-b141-2c41e93bccd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-7097-756f-b141-2c41e93bccd6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-7105-8e48-4a88a06d7c55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-7105-8e48-4a88a06d7c55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-7f76-94f0-b23338a659af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-7f76-94f0-b23338a659af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-7097-76e4-83fd-5745faf981cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-7097-76e4-83fd-5745faf981cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019dd5cd-3406-7526-953a-a01a47f5c5a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019dd5cd-3406-7526-953a-a01a47f5c5a8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dda1e-5b6f-70fa-8b8d-32ca9aa0bac8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7db0-96a4-33bdf0655893" xlink:to="loc_us-gaap_NetIncomeLoss_019dda1e-5b6f-70fa-8b8d-32ca9aa0bac8" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-7e32-8f65-b810b5e82e8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-7e32-8f65-b810b5e82e8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_019dd587-7097-7488-b8d5-e1ee9479fe06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_DebtCurrent_019dd587-7097-7488-b8d5-e1ee9479fe06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dd587-7097-7b1a-9554-f4e00a0f8d83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dd587-7097-7b1a-9554-f4e00a0f8d83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_019dd587-7097-783b-ab75-7744584ae280" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_TaxesPayableCurrent_019dd587-7097-783b-ab75-7744584ae280" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dd587-7097-7680-a3c6-31c73bb3f3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_InterestPayableCurrent_019dd587-7097-7680-a3c6-31c73bb3f3ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-7097-7e7e-b2be-c507689710cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-7097-7e7e-b2be-c507689710cc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-7097-70d0-a1d8-8a846d458548" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-7097-70d0-a1d8-8a846d458548" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-7097-75b4-9ae7-6fddf1db8e31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-7097-75b4-9ae7-6fddf1db8e31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dd587-7097-7819-ad86-81050b2478fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019dd587-7097-7818-9fb7-8384f7a5888e" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dd587-7097-7819-ad86-81050b2478fd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7097-7999-8036-c82fb8d27653" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7097-7999-8036-c82fb8d27653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-7097-7c73-9f69-ef89bd0d672a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-7097-7c73-9f69-ef89bd0d672a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-7097-7031-81ea-f57fb89fbfc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-7097-7031-81ea-f57fb89fbfc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-7097-73f4-8e28-94662347df15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-7097-73f4-8e28-94662347df15" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-7097-7e1c-b9b7-3ba78a755285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-7097-7e1c-b9b7-3ba78a755285" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-7097-749c-9983-e85f349b66ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-7097-749c-9983-e85f349b66ca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_019dd587-7097-7f24-9aeb-390a524cee61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019dd587-7097-7f14-8715-ff599b453bd1" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_019dd587-7097-7f24-9aeb-390a524cee61" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019dd587-7097-719d-a9d3-a7bed7cf4824" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019dd587-7097-719d-a9d3-a7bed7cf4824" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-7d22-bf93-604cc403d3ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-7d22-bf93-604cc403d3ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019dda3c-bc61-74c0-8496-26a77e243922" 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_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_SharesIssued_019dda3c-bc61-74c0-8496-26a77e243922" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-7097-7f0b-a5cc-85dff926ba21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:to="loc_us-gaap_CommonStockValue_019dd587-7097-7f0b-a5cc-85dff926ba21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-7969-916c-bc7d2a3b682d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-7969-916c-bc7d2a3b682d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-738f-9190-4479cf8ec104" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-738f-9190-4479cf8ec104" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7ad9-85af-8aded6bcea60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_019dd587-7097-76c2-961e-9434f04afdc1" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7ad9-85af-8aded6bcea60" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019dd5de-c807-7783-b10d-3d2765bf8f4b" 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_019dd587-7097-76c2-961e-9434f04afdc1" xlink:to="loc_us-gaap_StockholdersEquity_019dd5de-c807-7783-b10d-3d2765bf8f4b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dd587-7097-7bec-b366-3da4019744c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019dd587-7097-7c08-89cd-50aff1fda180" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019dd587-7097-7bec-b366-3da4019744c7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dd587-7097-7294-a923-ad2accb24678" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dd587-7097-7294-a923-ad2accb24678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-77d0-a15a-a55220274ee3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-77d0-a15a-a55220274ee3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019dd587-7097-764c-b772-f3a77bf36d84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_CommonStockSharesIssued_019dd587-7097-764c-b772-f3a77bf36d84" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dd587-7097-72ec-9ed0-b0d247b5248f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_Liabilities_019dd587-7097-72ec-9ed0-b0d247b5248f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019dd587-7097-72e1-a3b9-36ec78b2a4c6" 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_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AssetsCurrent_019dd587-7097-72e1-a3b9-36ec78b2a4c6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-76f0-963a-98e6ff2bdb8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-76f0-963a-98e6ff2bdb8d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-738d-adf8-836367a9d37e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-738d-adf8-836367a9d37e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019dd587-7097-7776-b270-a806c745bd2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_InventoryNet_019dd587-7097-7776-b270-a806c745bd2a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-7097-7a22-a543-a75e7fce3790" xlink:href="dpl-20260331.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-7097-7a22-a543-a75e7fce3790" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-7097-7bac-8c10-c6a8a97e5fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-7097-7bac-8c10-c6a8a97e5fc2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019dd587-7097-7b8b-937b-ef630a235804" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019dd587-7097-7b8b-937b-ef630a235804" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019dd587-7097-7c55-8dbc-6dc763605cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_OtherAssetsCurrent_019dd587-7097-7c55-8dbc-6dc763605cdc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-7097-72df-a5d3-e4bbeb8f42be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-7097-72df-a5d3-e4bbeb8f42be" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-7000-bfc7-1f1e05720e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-7000-bfc7-1f1e05720e5d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-7097-71be-bb72-04c897a36e3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-7097-71be-bb72-04c897a36e3f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dd587-7097-758c-a8a4-915dbe233c80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dd587-7097-758c-a8a4-915dbe233c80" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_019dd587-7097-775e-9517-721dc78467d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AssetsNoncurrent_019dd587-7097-775e-9517-721dc78467d8" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-7097-7129-9da4-52ac5001c191" 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_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_Assets_019dd587-7097-7129-9da4-52ac5001c191" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-7433-b29d-b0da39ab6a74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-7433-b29d-b0da39ab6a74" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-74c2-b837-b191ee7bafd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-74c2-b837-b191ee7bafd2" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7c3e-9132-001418d4f6b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7320-b79a-536538f42ddc" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7c3e-9132-001418d4f6b5" xlink:type="arc" order="21"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-755b-8471-ff9af831ae64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-755b-8471-ff9af831ae64" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-7ab8-ae1a-10fd32dbe482" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-7ab8-ae1a-10fd32dbe482" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019dd587-7097-7d7c-97f3-f51560115ff5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CommonStockSharesIssued_019dd587-7097-7d7c-97f3-f51560115ff5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dd587-7097-7fc4-894c-6bad89c80cd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dd587-7097-7fc4-894c-6bad89c80cd2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-7f69-8803-634f7ab05051" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-7f69-8803-634f7ab05051" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-7f5d-8d32-21da9ef6c4a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-7f5d-8d32-21da9ef6c4a0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-7904-a1bd-3945669a6053" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-7904-a1bd-3945669a6053" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-70d8-8763-aa86384f86f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-70d8-8763-aa86384f86f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-771a-8b07-dd9173702718" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-771a-8b07-dd9173702718" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019dd587-7097-7600-961d-a0a1f9ed56e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_InventoryNet_019dd587-7097-7600-961d-a0a1f9ed56e2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-7097-714a-8ad0-92eb4e2c6e93" xlink:href="dpl-20260331.xsd#dpl_TaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_dpl_TaxesApplicableToSubsequentYears_019dd587-7097-714a-8ad0-92eb4e2c6e93" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-7097-7ca4-a1f6-754eacc0acd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_019dd587-7097-7ca4-a1f6-754eacc0acd9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019dd587-7097-717d-ae19-419d607bf5c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019dd587-7097-717d-ae19-419d607bf5c6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019dd587-7097-74c9-b737-069c26a447ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_OtherAssetsCurrent_019dd587-7097-74c9-b737-069c26a447ce" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7707-89c3-d846c1e77dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7707-89c3-d846c1e77dc6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-75e3-a8df-22cec96ae7c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-75e3-a8df-22cec96ae7c6" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-7097-7a8d-9b02-5ed9ecfe5450" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019dd587-7097-7a8d-9b02-5ed9ecfe5450" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019dd587-7097-7ca6-a0c2-f5d72746b07c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019dd587-7097-7ca6-a0c2-f5d72746b07c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019dd587-7097-7574-b19d-ccdd7cebb32e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_LiabilitiesCurrent_019dd587-7097-7574-b19d-ccdd7cebb32e" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_019dd587-7097-7d3c-84fa-39c8511546d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_DebtCurrent_019dd587-7097-7d3c-84fa-39c8511546d8" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019dd587-7097-7b0c-8e64-8a955148d152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AccountsPayableCurrent_019dd587-7097-7b0c-8e64-8a955148d152" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrent_019dd587-7097-7b14-94f0-9f330470c63c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_TaxesPayableCurrent_019dd587-7097-7b14-94f0-9f330470c63c" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_019dd587-7097-7e2e-aa7d-a7c6b86b9a78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_InterestPayableCurrent_019dd587-7097-7e2e-aa7d-a7c6b86b9a78" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-7097-77a4-9e0d-e2c588f1e874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019dd587-7097-77a4-9e0d-e2c588f1e874" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-7097-72f0-b021-3988d62bbabf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_019dd587-7097-72f0-b021-3988d62bbabf" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-7097-7b95-9288-a10b2541b006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019dd587-7097-7b95-9288-a10b2541b006" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7097-7218-b2e8-dba9a1ea6ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7097-7218-b2e8-dba9a1ea6ef1" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-7097-794c-82c4-a5fe753e0c61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019dd587-7097-794c-82c4-a5fe753e0c61" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-7097-7e10-bbb1-1a72ff36c5de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_TaxesPayableCurrentAndNoncurrent_019dd587-7097-7e10-bbb1-1a72ff36c5de" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-7097-70a1-837d-a47608087abf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_019dd587-7097-70a1-837d-a47608087abf" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-7097-71cd-b1ee-e9906c9f349c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent_019dd587-7097-71cd-b1ee-e9906c9f349c" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-7097-7efd-b835-7acf89083d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019dd587-7097-7efd-b835-7acf89083d9d" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-7097-76de-b439-e0aef959ee16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_CommonStockValue_019dd587-7097-76de-b439-e0aef959ee16" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-79fb-b533-57d4dd9490dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-79fb-b533-57d4dd9490dc" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7a74-8aba-41ebf0ff41f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7a74-8aba-41ebf0ff41f4" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7591-998e-e39fa106d87e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7591-998e-e39fa106d87e" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019dd587-7097-7612-bd35-6a0778ec83d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-790b-a8a0-bed2899b900a" xlink:to="loc_us-gaap_Liabilities_019dd587-7097-7612-bd35-6a0778ec83d9" xlink:type="arc" order="35"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="dpl-20260331.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-70d5-bc5b-c62a659ca281" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-70d5-bc5b-c62a659ca281" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-7097-7a03-8be5-47b02524a469" 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_019dd587-7097-78eb-97d6-6597396da200" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-7097-7a03-8be5-47b02524a469" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_019dd587-7097-7710-9327-77cd40963638" xlink:href="dpl-20260331.xsd#dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_dpl_DepreciationDepletionandAmortizationIncludingDiscontinuedOperation_019dd587-7097-7710-9327-77cd40963638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dd587-7097-7f1b-8d33-7c3dfd596747" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_us-gaap_AmortizationOfFinancingCostsAndDiscounts_019dd587-7097-7f1b-8d33-7c3dfd596747" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation_019dd587-7097-7bab-8710-3d0f1e2a6fa9" xlink:href="dpl-20260331.xsd#dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_dpl_GainLossOnDispositionOfBusinessIncludingDiscontinuedOperation_019dd587-7097-7bab-8710-3d0f1e2a6fa9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_019dd587-7097-7bc0-856a-d27669a7caf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionAdditions_019dd587-7097-7bc0-856a-d27669a7caf7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInReceivables_019dd587-7097-7b2f-8563-09c4f98ee411" 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_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_us-gaap_IncreaseDecreaseInReceivables_019dd587-7097-7b2f-8563-09c4f98ee411" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_019dd587-7097-7443-9460-50db2e1d9fe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_019dd587-7097-7443-9460-50db2e1d9fe5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-7f64-91f3-091a7207b5f5" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_019dd587-7097-7276-8141-e911fddc4dcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_019dd587-7097-7276-8141-e911fddc4dcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_019dd587-7097-78b9-9a55-d2675c8f6b4b" xlink:href="dpl-20260331.xsd#dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_dpl_IncreaseDecreaseInTaxesApplicableToSubsequentYears_019dd587-7097-78b9-9a55-d2675c8f6b4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_019dd587-7097-747a-bc03-067042c7d104" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidExpense_019dd587-7097-747a-bc03-067042c7d104" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019dd587-7097-772d-a6d8-4f7f314d76c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019dd587-7097-772d-a6d8-4f7f314d76c3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dd587-7097-7e35-92d9-572250f4e401" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019dd587-7097-7e35-92d9-572250f4e401" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019dd587-7097-76be-82a6-6d60cab90ca1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_019dd587-7097-76be-82a6-6d60cab90ca1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dd587-7097-7f91-ae1b-0af7ed445dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_019dd587-7097-7f91-ae1b-0af7ed445dcb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019dd587-7097-74a8-a0f4-4db89ef81bc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019dd587-7097-74a8-a0f4-4db89ef81bc5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_019dd587-7097-7949-a3b4-6cf062671a72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInPensionAndPostretirementObligations_019dd587-7097-7949-a3b4-6cf062671a72" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_019dd587-7097-783a-9138-f820eddeacaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_019dd587-7097-7309-9fa1-8550ffbb2f81" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_019dd587-7097-783a-9138-f820eddeacaf" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dd587-7097-79d9-8c2b-3dca6029a1ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019dd587-7097-79d9-8c2b-3dca6029a1ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireProductiveAssets_019dd587-7097-7f0e-ac96-f1cc26f250db" 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_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:to="loc_us-gaap_PaymentsToAcquireProductiveAssets_019dd587-7097-7f0e-ac96-f1cc26f250db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_019dd5d5-1f35-7b24-a51e-897d6ff68922" 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_NetCashProvidedByUsedInOperatingActivitiesAbstract_019dd587-7097-78eb-97d6-6597396da200" xlink:to="loc_us-gaap_ProceedsFromContributionInAidOfConstruction_019dd5d5-1f35-7b24-a51e-897d6ff68922" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-7097-7700-970d-e4bc928149e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-7097-7700-970d-e4bc928149e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates_019dd587-7097-7a23-bd65-ef674d92ce1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:to="loc_us-gaap_PaymentsForProceedsFromBusinessesAndInterestInAffiliates_019dd587-7097-7a23-bd65-ef674d92ce1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dd587-7097-7d31-b052-0496df19cb84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_019dd587-7097-7d31-b052-0496df19cb84" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dd587-7097-707a-abe0-90d0894f010b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_019dd587-7097-703d-a153-32f4945ac2db" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019dd587-7097-707a-abe0-90d0894f010b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019dd587-7097-7d22-9797-bf0400a41597" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_PaymentsOfDividends_019dd587-7097-7d22-9797-bf0400a41597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfOrdinaryDividends_019dd5d7-0620-7a72-8c5f-78415cfde494" 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_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_PaymentsOfOrdinaryDividends_019dd5d7-0620-7a72-8c5f-78415cfde494" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PaymentsOfDeferredFinanceCosts_019dd587-7097-7510-b7b9-b403e54c954c" xlink:href="dpl-20260331.xsd#dpl_PaymentsOfDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_dpl_PaymentsOfDeferredFinanceCosts_019dd587-7097-7510-b7b9-b403e54c954c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019dd587-7097-7daa-8166-6b8d113537a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019dd587-7097-7daa-8166-6b8d113537a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_019dd587-7097-7e81-b93a-95eaf6d404ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_019dd587-7097-7e81-b93a-95eaf6d404ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromShortTermDebt_019dd587-7097-7ee3-83ea-4c56704a9381" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_ProceedsFromShortTermDebt_019dd587-7097-7ee3-83ea-4c56704a9381" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfShortTermDebt_019dd587-7097-7807-a267-81be46ed4e72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_RepaymentsOfShortTermDebt_019dd587-7097-7807-a267-81be46ed4e72" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7097-7782-8277-490e5a64f055" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7097-7782-8277-490e5a64f055" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dd587-7097-7510-b083-151b45954033" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_019dd587-7097-7834-960e-46aaf13368b1" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019dd587-7097-7510-b083-151b45954033" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-7097-7fd5-9b6d-50ee27eac737" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-7097-7fd5-9b6d-50ee27eac737" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dd587-7097-7aac-af25-ae6556b09c83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-7097-7fd5-9b6d-50ee27eac737" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019dd587-7097-7aac-af25-ae6556b09c83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-7097-7034-8397-df5ff0a2d5fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019dd587-7097-7fd5-9b6d-50ee27eac737" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-7097-7034-8397-df5ff0a2d5fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_019dd587-7097-7e85-98b7-b2d48bda2d54" 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_019dd587-7097-7fd5-9b6d-50ee27eac737" xlink:to="loc_us-gaap_InterestPaidNet_019dd587-7097-7e85-98b7-b2d48bda2d54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-7097-7337-9059-1243bf850a84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-7097-7337-9059-1243bf850a84" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019dd587-7097-7516-8ae1-c26bdfe8d313" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019dd587-7097-7337-9059-1243bf850a84" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019dd587-7097-7516-8ae1-c26bdfe8d313" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-7097-7a03-b5fd-66dd11eb67c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-7097-7a03-b5fd-66dd11eb67c7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019dd587-7097-785d-832c-506b823a1387" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019dd587-7097-7a03-b5fd-66dd11eb67c7" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019dd587-7097-785d-832c-506b823a1387" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019dd587-7097-727e-ad5a-60effe8139bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_019dd587-7097-727e-ad5a-60effe8139bc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInSecurityDeposits_019dd587-7097-7973-8daa-fd417f8c87ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInSecurityDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_IncreaseDecreaseInSecurityDeposits_019dd587-7097-7973-8daa-fd417f8c87ea" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromInsuranceSettlementInvestingActivities_019dd587-7097-788f-86e2-e68865b5e5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromInsuranceSettlementInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_ProceedsFromInsuranceSettlementInvestingActivities_019dd587-7097-788f-86e2-e68865b5e5a3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dd587-7097-7d7e-8d18-6a9447ce4e88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_019dd587-7097-7d7e-8d18-6a9447ce4e88" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NonCashProceedsFromSaleOfBusiness_019dd587-7097-7d63-8df4-3b8c9eb52da4" xlink:href="dpl-20260331.xsd#dpl_NonCashProceedsFromSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_dpl_NonCashProceedsFromSaleOfBusiness_019dd587-7097-7d63-8df4-3b8c9eb52da4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dd587-7097-79c8-9c78-cfca6d9bdb66" 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_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019dd587-7097-79c8-9c78-cfca6d9bdb66" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_019dd587-7097-7555-a20d-386f4274cb6d" 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_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities_019dd587-7097-7555-a20d-386f4274cb6d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_019dd587-7097-7909-9be4-379a8fa81760" xlink:href="dpl-20260331.xsd#dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_dpl_IncreaseDecreaseInCurrentRegulatoryAssetsAndLiabilities_019dd587-7097-7909-9be4-379a8fa81760" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dd587-7097-7b70-9bc5-8da76710de85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7903-a20a-cd275c637b49" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_019dd587-7097-7b70-9bc5-8da76710de85" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/StatementofShareholdersEquityStatement" xlink:type="simple" xlink:href="dpl-20260331.xsd#StatementofShareholdersEquityStatement"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/StatementofShareholdersEquityStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-7b86-97e7-413ac7948548" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-7b86-97e7-413ac7948548" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-709b-ab76-be8dcd4982e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-7b86-97e7-413ac7948548" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-709b-ab76-be8dcd4982e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-709b-ab76-be8dcd4982e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-709b-ab76-be8dcd4982e0" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-709b-ab76-be8dcd4982e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-709b-ab76-be8dcd4982e0" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019dd587-7097-7ab1-af8d-32a2ad96e285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:to="loc_us-gaap_CommonStockMember_019dd587-7097-7ab1-af8d-32a2ad96e285" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-7097-7ee3-8f40-eb0d4edab252" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAdditionalCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-7097-7ee3-8f40-eb0d4edab252" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-7097-743f-a889-02e728c1f628" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019dd587-7097-743f-a889-02e728c1f628" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019dd587-7097-739e-a231-e49d8f7a11ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:to="loc_us-gaap_RetainedEarningsMember_019dd587-7097-739e-a231-e49d8f7a11ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019dd5fb-4a11-70c4-8480-e7c1163118b2" 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_019dd587-7097-7e02-9dec-aea5b2ab8f9c" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019dd5fb-4a11-70c4-8480-e7c1163118b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_019dd587-7097-76e0-a692-37b580bfbff6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_SharesIssued_019dd587-7097-76e0-a692-37b580bfbff6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-723c-872b-6471b6494a66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-723c-872b-6471b6494a66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e05-8ffc-4ce1a14d50e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e05-8ffc-4ce1a14d50e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfOrdinaryDividends_019dd5fe-d47a-7690-ab47-9568ab058179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfOrdinaryDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_PaymentsOfOrdinaryDividends_019dd5fe-d47a-7690-ab47-9568ab058179" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-7097-7214-8825-309572f6f5fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_ProfitLoss_019dd587-7097-7214-8825-309572f6f5fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-7c78-80b2-71f42a5f1419" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_019dd587-7097-7c78-80b2-71f42a5f1419" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-78b0-bcae-13c9deb61bfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019dd587-7097-78b0-bcae-13c9deb61bfb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019dd587-7097-7780-8e1b-3043804eb4d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_CommonStockValue_019dd587-7097-7780-8e1b-3043804eb4d0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-7b6c-8b85-f903e32330db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019dd587-7097-7b6c-8b85-f903e32330db" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e82-8e5f-a04b2d9cf8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7e82-8e5f-a04b2d9cf8d7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7e50-88e9-9f3e87da1e52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019dd587-7097-7e50-88e9-9f3e87da1e52" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dd587-7097-744f-b489-bca178317408" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_StockholdersEquityOther_019dd587-7097-744f-b489-bca178317408" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-73dc-a432-afb26135a0ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019dd587-7097-73dc-a432-afb26135a0ce" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividends_019dd587-7097-74e6-bb72-40308e3ee595" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_PaymentsOfDividends_019dd587-7097-74e6-bb72-40308e3ee595" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-7097-78b4-af9f-114d714343af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-7097-78b4-af9f-114d714343af" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-7097-7e8b-a775-efc21108519a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-7097-7e8b-a775-efc21108519a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019dd5df-fa43-74b2-a0ff-8f3c85b3bb9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_StockholdersEquity_019dd5df-fa43-74b2-a0ff-8f3c85b3bb9a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019dd5f4-f992-7cb1-a6a3-bb0598943f6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-773e-8a42-c62c21c666c2" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019dd5f4-f992-7cb1-a6a3-bb0598943f6c" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/OverviewandSummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="dpl-20260331.xsd#OverviewandSummaryofSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/OverviewandSummaryofSignificantAccountingPolicies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7c66-aae6-fd0e2d22e936" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7d63-b3b3-cd4e5abcc5eb" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7c66-aae6-fd0e2d22e936" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7d63-b3b3-cd4e5abcc5eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7714-8c48-c66f8d441205" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7d63-b3b3-cd4e5abcc5eb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7714-8c48-c66f8d441205" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7714-8c48-c66f8d441205_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7714-8c48-c66f8d441205" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7714-8c48-c66f8d441205_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7ae6-b572-deb1ab393ed0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7714-8c48-c66f8d441205" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7ae6-b572-deb1ab393ed0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-7316-9225-77660c70085d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7ae6-b572-deb1ab393ed0" xlink:to="loc_srt_SubsidiariesMember_019dd587-7097-7316-9225-77660c70085d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantAccountingPoliciesTextBlock_019dd587-7097-79da-9f38-e5209957507b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SignificantAccountingPoliciesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7c66-aae6-fd0e2d22e936" xlink:to="loc_us-gaap_SignificantAccountingPoliciesTextBlock_019dd587-7097-79da-9f38-e5209957507b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RegulatoryMattersNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RegulatoryMattersNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7101-bf23-09c5f2361ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-7a71-885c-c6d74ee04dfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7101-bf23-09c5f2361ae9" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-7a71-885c-c6d74ee04dfb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-7097-7a63-a0aa-696dbc7c1ba2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7101-bf23-09c5f2361ae9" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-7097-7a63-a0aa-696dbc7c1ba2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValue" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValue"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValue" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-769b-ba5b-3ba4361813c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-7097-74f3-8a51-085bc2a61bce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-769b-ba5b-3ba4361813c3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-7097-74f3-8a51-085bc2a61bce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_019dd587-7097-7ce2-b2ae-ab5d902e7aea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-769b-ba5b-3ba4361813c3" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_019dd587-7097-7ce2-b2ae-ab5d902e7aea" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtObligations" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtObligations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtObligations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e81-b9b2-e6b455f74057" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7ce8-9f15-758a8d3b8f04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e81-b9b2-e6b455f74057" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7ce8-9f15-758a8d3b8f04" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_019dd587-7098-731b-a41a-7e9559038901" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e81-b9b2-e6b455f74057" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_019dd587-7098-731b-a41a-7e9559038901" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxes" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-7f61-9dd8-107dd3a37f69" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-749b-a28e-f223cc23f80d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7f61-9dd8-107dd3a37f69" xlink:to="loc_dei_EntitiesTable_019dd587-7098-749b-a28e-f223cc23f80d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7a7f-9945-d7b7a573488d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-749b-a28e-f223cc23f80d" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7a7f-9945-d7b7a573488d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7a7f-9945-d7b7a573488d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7a7f-9945-d7b7a573488d" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7a7f-9945-d7b7a573488d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-78bd-9238-83f4eb169629" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7a7f-9945-d7b7a573488d" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-78bd-9238-83f4eb169629" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7852-aa41-676a0736ce32" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-78bd-9238-83f4eb169629" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7852-aa41-676a0736ce32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock_019dd587-7098-7c68-8691-983f78fb3165" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7f61-9dd8-107dd3a37f69" xlink:to="loc_us-gaap_IncomeTaxDisclosureTextBlock_019dd587-7098-7c68-8691-983f78fb3165" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlans" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlans"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlans" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-7e26-934a-f97845b18825" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-72f2-863e-e5a36863ea75" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7e26-934a-f97845b18825" xlink:to="loc_dei_EntitiesTable_019dd587-7098-72f2-863e-e5a36863ea75" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-77bb-80f2-95a72b917144" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-72f2-863e-e5a36863ea75" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-77bb-80f2-95a72b917144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-77bb-80f2-95a72b917144_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-77bb-80f2-95a72b917144" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-77bb-80f2-95a72b917144_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-755d-97c7-8b6e03641cb3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-77bb-80f2-95a72b917144" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-755d-97c7-8b6e03641cb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-72b2-847e-f6d011b32b67" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-755d-97c7-8b6e03641cb3" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-72b2-847e-f6d011b32b67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7c95-b500-1c7fbda4afa1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-72f2-863e-e5a36863ea75" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7c95-b500-1c7fbda4afa1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7c95-b500-1c7fbda4afa1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7c95-b500-1c7fbda4afa1" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7c95-b500-1c7fbda4afa1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7b96-ab9b-f26930b5a215" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7c95-b500-1c7fbda4afa1" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7b96-ab9b-f26930b5a215" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-73e9-8afe-47d48336504f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7b96-ab9b-f26930b5a215" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-73e9-8afe-47d48336504f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_019dd587-7098-75bf-b063-3d99f639685c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7e26-934a-f97845b18825" xlink:to="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_019dd587-7098-75bf-b063-3d99f639685c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingencies" xlink:type="simple" xlink:href="dpl-20260331.xsd#ContractualObligationsCommercialCommitmentsandContingencies"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingencies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-7dc6-bcc6-57618c223de6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-7895-853a-cd5507b89227" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7dc6-bcc6-57618c223de6" xlink:to="loc_dei_EntitiesTable_019dd587-7098-7895-853a-cd5507b89227" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-777f-b97d-04da6c9180ba" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-7895-853a-cd5507b89227" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-777f-b97d-04da6c9180ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-777f-b97d-04da6c9180ba_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-777f-b97d-04da6c9180ba" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-777f-b97d-04da6c9180ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-77de-8f68-770dbd845412" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-777f-b97d-04da6c9180ba" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-77de-8f68-770dbd845412" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7dbf-ac3f-09c44ce60708" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-77de-8f68-770dbd845412" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7dbf-ac3f-09c44ce60708" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_019dd587-7098-7d0d-8be4-683fee41714b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7dc6-bcc6-57618c223de6" xlink:to="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_019dd587-7098-7d0d-8be4-683fee41714b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegments" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegments"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegments" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7e8b-afc0-0782a0550d70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7e8b-afc0-0782a0550d70" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ff5-93bf-b0c13fb52932" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ff5-93bf-b0c13fb52932" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7ff5-93bf-b0c13fb52932_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ff5-93bf-b0c13fb52932" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7ff5-93bf-b0c13fb52932_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7fdd-b1bd-56a0d8c42670" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ff5-93bf-b0c13fb52932" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7fdd-b1bd-56a0d8c42670" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7613-a302-d4c909fd6ed3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7fdd-b1bd-56a0d8c42670" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7613-a302-d4c909fd6ed3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-7098-7982-aec6-f82114040b39" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-7098-7982-aec6-f82114040b39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-7098-7982-aec6-f82114040b39_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-7098-7982-aec6-f82114040b39" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-7098-7982-aec6-f82114040b39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-7098-7e70-aaa4-96349c18cf31" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-7098-7982-aec6-f82114040b39" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-7098-7e70-aaa4-96349c18cf31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019dd587-7098-77e6-997d-3ccf78b772c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:to="loc_us-gaap_SubsegmentsAxis_019dd587-7098-77e6-997d-3ccf78b772c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-7098-77e6-997d-3ccf78b772c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-7098-77e6-997d-3ccf78b772c1" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-7098-77e6-997d-3ccf78b772c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-7098-73a9-a8f5-50e5cb61763a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-7098-77e6-997d-3ccf78b772c1" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-7098-73a9-a8f5-50e5cb61763a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-7098-7a34-8e65-91ea3b8524f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-7098-7a96-8047-ee9bbb289dd6" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-7098-7a34-8e65-91ea3b8524f6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-7098-7a34-8e65-91ea3b8524f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-7098-7a34-8e65-91ea3b8524f6" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-7098-7a34-8e65-91ea3b8524f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-7098-7d73-9a69-d792f9fbd16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-7098-7a34-8e65-91ea3b8524f6" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-7098-7d73-9a69-d792f9fbd16e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_019dd587-714d-737e-830f-426eab541ef6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7e8b-afc0-0782a0550d70" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_019dd587-714d-737e-830f-426eab541ef6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-714d-7dee-8697-97f71471682e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-714d-738f-b32f-5084b3df17bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-7dee-8697-97f71471682e" xlink:to="loc_us-gaap_StatementTable_019dd587-714d-738f-b32f-5084b3df17bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e81-b9c7-43d21591c0a5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-738f-b32f-5084b3df17bf" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e81-b9c7-43d21591c0a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e81-b9c7-43d21591c0a5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e81-b9c7-43d21591c0a5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e81-b9c7-43d21591c0a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f03-95b3-a542309ec037" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e81-b9c7-43d21591c0a5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f03-95b3-a542309ec037" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7c9e-b0c5-9ecec7c4328c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f03-95b3-a542309ec037" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7c9e-b0c5-9ecec7c4328c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_019dd587-714d-7665-b33b-0404ebaf27b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-7dee-8697-97f71471682e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_019dd587-714d-7665-b33b-0404ebaf27b0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FixedassetImpairmentNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#FixedassetImpairmentNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FixedassetImpairmentNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dd587-714d-70cb-9654-2bb03775f0b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-714d-78fe-b5b6-3669e5854afc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019dd587-714d-70cb-9654-2bb03775f0b2" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-714d-78fe-b5b6-3669e5854afc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7bf0-89b8-41bedb0d56aa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019dd587-714d-78fe-b5b6-3669e5854afc" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7bf0-89b8-41bedb0d56aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7bf0-89b8-41bedb0d56aa_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7bf0-89b8-41bedb0d56aa" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7bf0-89b8-41bedb0d56aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7586-bacd-4a665527e78c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7bf0-89b8-41bedb0d56aa" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7586-bacd-4a665527e78c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7ac8-a66c-fb8b8d39e302" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7586-bacd-4a665527e78c" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7ac8-a66c-fb8b8d39e302" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperations" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperations"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-773d-93f0-7383d3dc15b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-773d-93f0-7383d3dc15b9" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-75c0-8c02-dbde093b63e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-75c0-8c02-dbde093b63e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7581-be9c-f01d2d1c428f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7581-be9c-f01d2d1c428f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-751a-8d9c-84ff36463c7b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-751a-8d9c-84ff36463c7b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-74cb-853e-a77f5bcee12d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-74cb-853e-a77f5bcee12d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-7404-a448-cfe66fdff165" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-7404-a448-cfe66fdff165" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperations_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperations_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperations_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-773d-93f0-7383d3dc15b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-773d-93f0-7383d3dc15b9" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-75c0-8c02-dbde093b63e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-75c0-8c02-dbde093b63e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7581-be9c-f01d2d1c428f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-75c0-8c02-dbde093b63e7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7581-be9c-f01d2d1c428f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-729f-9b4e-7357d86e1136" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-751a-8d9c-84ff36463c7b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-751a-8d9c-84ff36463c7b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-74cb-853e-a77f5bcee12d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-751a-8d9c-84ff36463c7b" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-74cb-853e-a77f5bcee12d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RiskUncertaintiesNotes" xlink:type="simple" xlink:href="dpl-20260331.xsd#RiskUncertaintiesNotes"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RiskUncertaintiesNotes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-714d-75f6-9575-9ddd95c42a92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-75c5-b8b8-db55047efbe4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-714d-75f6-9575-9ddd95c42a92" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-75c5-b8b8-db55047efbe4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7656-82e3-8b83c66bc938" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-75c5-b8b8-db55047efbe4" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7656-82e3-8b83c66bc938" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7656-82e3-8b83c66bc938_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7656-82e3-8b83c66bc938" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7656-82e3-8b83c66bc938_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70eb-86d9-773783ec4497" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7656-82e3-8b83c66bc938" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70eb-86d9-773783ec4497" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7925-a38e-33dfeace7256" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70eb-86d9-773783ec4497" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7925-a38e-33dfeace7256" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-714d-7426-a3cb-46ec7767f4fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-75c5-b8b8-db55047efbe4" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-714d-7426-a3cb-46ec7767f4fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-714d-7426-a3cb-46ec7767f4fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-714d-7426-a3cb-46ec7767f4fa" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-714d-7426-a3cb-46ec7767f4fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-714d-73a3-9b0a-0f762ad0a5d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_019dd587-714d-7426-a3cb-46ec7767f4fa" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_019dd587-714d-73a3-9b0a-0f762ad0a5d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RisksandUncertaintiesTextBlock_019dd587-714d-7e00-85d2-ac1d61903022" xlink:href="dpl-20260331.xsd#dpl_RisksandUncertaintiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-714d-75f6-9575-9ddd95c42a92" xlink:to="loc_dpl_RisksandUncertaintiesTextBlock_019dd587-714d-7e00-85d2-ac1d61903022" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesPolicy" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesPolicy"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesPolicy" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-72a5-a363-af3a29e7b1db" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-72a5-a363-af3a29e7b1db" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryPolicyTextBlock_019dd587-7097-7fc0-8070-cd1f09f7fc9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_us-gaap_InventoryPolicyTextBlock_019dd587-7097-7fc0-8070-cd1f09f7fc9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NatureOfOperations_019dd587-7097-7bdc-89d1-8d6d020a992a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NatureOfOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_us-gaap_NatureOfOperations_019dd587-7097-7bdc-89d1-8d6d020a992a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_019dd587-7097-73bf-8453-5726fa581cfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_019dd587-7097-73bf-8453-5726fa581cfe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryIncomeTaxesPolicy_019dd587-7097-721d-a2b0-7245a23d3d58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryIncomeTaxesPolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_us-gaap_RegulatoryIncomeTaxesPolicy_019dd587-7097-721d-a2b0-7245a23d3d58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-7097-7e81-8256-6c75418603da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-7beb-98d3-d9e34ae26092" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-7097-7e81-8256-6c75418603da" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dd587-7097-7b9b-9037-dfeb3ea5072e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019dd587-7097-7b9b-9037-dfeb3ea5072e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_019dd587-7097-7809-8b7a-ab632b56a575" xlink:href="dpl-20260331.xsd#dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionCapitalizedInterestTableTextBlock_019dd587-7097-7809-8b7a-ab632b56a575" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_019dd587-7097-735e-8f12-c070699af5e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_019dd587-7097-735e-8f12-c070699af5e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_019dd587-7097-7ce8-a191-90d9bfe38f75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_019dd587-7097-7ce8-a191-90d9bfe38f75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_019dd587-7097-75ee-9c7e-fc9b84e98e69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_019dd587-7097-75ee-9c7e-fc9b84e98e69" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_019dd587-7097-7d03-bb31-01db9742face" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_AccountsReceivableAllowanceForCreditLossTableTextBlock_019dd587-7097-7d03-bb31-01db9742face" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-7097-7641-b082-0ad59c1b29fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_019dd587-7097-7641-b082-0ad59c1b29fc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_019dd587-7097-751a-90f9-7a02e8cffb9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTableTextBlock_019dd587-7097-751a-90f9-7a02e8cffb9f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_019dd587-7097-7a90-88bc-294639dcec6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019dd587-7097-78f5-b539-0fc581443623" xlink:to="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_019dd587-7097-7a90-88bc-294639dcec6e" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-7097-7465-ac27-0bfb65b5ba5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019dd587-7097-7465-ac27-0bfb65b5ba5d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_019dd587-7097-7ded-aee8-b11a8b144a24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_019dd587-7097-7ded-aee8-b11a8b144a24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_019dd587-7097-78d7-8c37-4bdb53c07b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_019dd587-7097-78d7-8c37-4bdb53c07b0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock_019dd587-7097-7917-a72c-d21cc2f4652f" xlink:href="dpl-20260331.xsd#dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:to="loc_dpl_ScheduleOfFairValueAndCostOfNonDerivativeInstrumentsTableTextBlock_019dd587-7097-7917-a72c-d21cc2f4652f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_019dd587-7097-7dbc-a45f-7b529a16af41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019dd587-7097-7045-bcca-46861ba8c613" xlink:to="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_019dd587-7097-7dbc-a45f-7b529a16af41" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e16-8c76-6b405186f290" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7540-8b6f-4374e1f7c81e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e16-8c76-6b405186f290" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7540-8b6f-4374e1f7c81e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_019dd587-7098-73fd-b586-969996f74cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e16-8c76-6b405186f290" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_019dd587-7098-73fd-b586-969996f74cc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_019dd587-7098-772a-9982-f3c465850bb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDebtInstrumentsTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e16-8c76-6b405186f290" xlink:to="loc_us-gaap_ScheduleOfDebtInstrumentsTextBlock_019dd587-7098-772a-9982-f3c465850bb1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxesTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-78a1-8bb2-5e438a890df8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-7f58-915f-97bd228b48ab" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-78a1-8bb2-5e438a890df8" xlink:to="loc_dei_EntitiesTable_019dd587-7098-7f58-915f-97bd228b48ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7e10-9c45-13db10d6b46e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-7f58-915f-97bd228b48ab" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7e10-9c45-13db10d6b46e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7e10-9c45-13db10d6b46e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7e10-9c45-13db10d6b46e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7e10-9c45-13db10d6b46e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-73e5-959b-5f8f696f12ab" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7e10-9c45-13db10d6b46e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-73e5-959b-5f8f696f12ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-74fb-ba7c-b29cdb37389f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-73e5-959b-5f8f696f12ab" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-74fb-ba7c-b29cdb37389f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-75b9-9ce8-e08b52e4b739" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-782d-bab0-ce4db7caddaa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-75b9-9ce8-e08b52e4b739" xlink:to="loc_dei_EntitiesTable_019dd587-7098-782d-bab0-ce4db7caddaa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ae5-abf7-8890efd5ad8c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-782d-bab0-ce4db7caddaa" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ae5-abf7-8890efd5ad8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7ae5-abf7-8890efd5ad8c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ae5-abf7-8890efd5ad8c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7ae5-abf7-8890efd5ad8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7d5b-b3de-6b25de47337c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7ae5-abf7-8890efd5ad8c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7d5b-b3de-6b25de47337c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-79b7-a2e8-925c29df479a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7d5b-b3de-6b25de47337c" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-79b7-a2e8-925c29df479a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_019dd587-7098-7c97-9785-d7f1f7f06365" xlink:href="dpl-20260331.xsd#dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-75b9-9ce8-e08b52e4b739" xlink:to="loc_dpl_ScheduleofNetPeriodicBenefitCostIncomeTableTextBlock_019dd587-7098-7c97-9785-d7f1f7f06365" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-72e4-85b6-4f969fd82c96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-72e4-85b6-4f969fd82c96" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-703d-910f-c87017b23d0e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-703d-910f-c87017b23d0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-703d-910f-c87017b23d0e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-703d-910f-c87017b23d0e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-703d-910f-c87017b23d0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7189-9ecc-d5e629641259" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-703d-910f-c87017b23d0e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7189-9ecc-d5e629641259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7e59-bb75-ac395291c5f5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7189-9ecc-d5e629641259" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7e59-bb75-ac395291c5f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-714d-75d7-b826-b9916a29aa38" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-714d-75d7-b826-b9916a29aa38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-75d7-b826-b9916a29aa38_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-75d7-b826-b9916a29aa38" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-75d7-b826-b9916a29aa38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-7fcc-babb-d9e52a17394f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-75d7-b826-b9916a29aa38" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-7fcc-babb-d9e52a17394f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019dd587-714d-7dc5-867b-035990492980" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:to="loc_us-gaap_SubsegmentsAxis_019dd587-714d-7dc5-867b-035990492980" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-714d-7dc5-867b-035990492980_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-714d-7dc5-867b-035990492980" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-714d-7dc5-867b-035990492980_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019dd587-714d-7a6e-91e0-e0bede11171f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019dd587-714d-7dc5-867b-035990492980" xlink:to="loc_us-gaap_SubsegmentsDomain_019dd587-714d-7a6e-91e0-e0bede11171f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-714d-73f3-9dd5-04a48a995b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-76be-950e-0bec86c5b1f9" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-714d-73f3-9dd5-04a48a995b1f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-714d-73f3-9dd5-04a48a995b1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-714d-73f3-9dd5-04a48a995b1f" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-714d-73f3-9dd5-04a48a995b1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-714d-7d62-b52b-3338d24b5cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsConsolidationItemsAxis_019dd587-714d-73f3-9dd5-04a48a995b1f" xlink:to="loc_us-gaap_SubsegmentsConsolidationItemsDomain_019dd587-714d-7d62-b52b-3338d24b5cdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_019dd587-714d-74f7-84cf-ffcc0f48e91c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-72e4-85b6-4f969fd82c96" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_019dd587-714d-74f7-84cf-ffcc0f48e91c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-714d-7c83-8f4e-d622d94ef698" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-714d-7f46-a543-a8e1290128d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-7c83-8f4e-d622d94ef698" xlink:to="loc_us-gaap_StatementTable_019dd587-714d-7f46-a543-a8e1290128d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7cd1-9f93-03ae8a041338" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7f46-a543-a8e1290128d5" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7cd1-9f93-03ae8a041338" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7cd1-9f93-03ae8a041338_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7cd1-9f93-03ae8a041338" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7cd1-9f93-03ae8a041338_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70df-bbf8-65dc448f0f66" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7cd1-9f93-03ae8a041338" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70df-bbf8-65dc448f0f66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7f0a-8111-b913dc2bd06b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-70df-bbf8-65dc448f0f66" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7f0a-8111-b913dc2bd06b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_019dd587-714d-77f9-87d7-8d2bee586a69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-7c83-8f4e-d622d94ef698" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_019dd587-714d-77f9-87d7-8d2bee586a69" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsTables" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsTables"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-7e6b-8adf-baccb4d4135b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-7e6b-8adf-baccb4d4135b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7f54-859c-f6d351069526_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7f54-859c-f6d351069526_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-77d4-aa94-b64b5094b2c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-77d4-aa94-b64b5094b2c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70f7-8327-7abbdc60c1b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70f7-8327-7abbdc60c1b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70d7-ae9c-3dcac9168d42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70d7-ae9c-3dcac9168d42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-794e-a099-aba4efd11489" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-794e-a099-aba4efd11489" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsTables_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsTables_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsTables_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-7e6b-8adf-baccb4d4135b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-7e6b-8adf-baccb4d4135b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7f54-859c-f6d351069526_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7f54-859c-f6d351069526_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-77d4-aa94-b64b5094b2c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-7f54-859c-f6d351069526" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-77d4-aa94-b64b5094b2c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7ba1-a89e-3e4802bcb1a6" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70f7-8327-7abbdc60c1b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70f7-8327-7abbdc60c1b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70d7-ae9c-3dcac9168d42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-70f7-8327-7abbdc60c1b9" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-70d7-ae9c-3dcac9168d42" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:href="dpl-20260331.xsd#dpl_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dd587-7097-7b06-8c31-4301fe1a9d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_us-gaap_CreditFacilityAxis_019dd587-7097-7b06-8c31-4301fe1a9d6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd587-7097-7b06-8c31-4301fe1a9d6b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd587-7097-7b06-8c31-4301fe1a9d6b" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd587-7097-7b06-8c31-4301fe1a9d6b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dd587-7097-7785-b1f6-ac41a81cd11e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dd587-7097-7b06-8c31-4301fe1a9d6b" xlink:to="loc_us-gaap_CreditFacilityDomain_019dd587-7097-7785-b1f6-ac41a81cd11e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-748f-8480-aff24a7a9cd3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-748f-8480-aff24a7a9cd3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-748f-8480-aff24a7a9cd3_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-748f-8480-aff24a7a9cd3" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-748f-8480-aff24a7a9cd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7198-b18e-f8599b2a829e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-748f-8480-aff24a7a9cd3" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7198-b18e-f8599b2a829e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-77e1-a528-c285abbe3d39" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7198-b18e-f8599b2a829e" xlink:to="loc_srt_SubsidiariesMember_019dd587-7097-77e1-a528-c285abbe3d39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-719c-a5f4-bee4149b9e08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-719c-a5f4-bee4149b9e08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-719c-a5f4-bee4149b9e08_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-719c-a5f4-bee4149b9e08" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-719c-a5f4-bee4149b9e08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7e2d-aeb0-e8f9a7ad012a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019dd587-7097-719c-a5f4-bee4149b9e08" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7e2d-aeb0-e8f9a7ad012a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-7097-7a2e-b638-9f32346f90b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019dd587-7097-7e2d-aeb0-e8f9a7ad012a" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019dd587-7097-7a2e-b638-9f32346f90b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-76e0-9cf2-141fcaaf6067" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-76e0-9cf2-141fcaaf6067" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-76e0-9cf2-141fcaaf6067_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-76e0-9cf2-141fcaaf6067" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-76e0-9cf2-141fcaaf6067_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7097-7352-bb00-06d598e1f019" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7097-76e0-9cf2-141fcaaf6067" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7097-7352-bb00-06d598e1f019" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7097-7ed2-abc0-9ade43baa0c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7097-7352-bb00-06d598e1f019" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7097-7ed2-abc0-9ade43baa0c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7a02-96cd-2fada8f345b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7a02-96cd-2fada8f345b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7a02-96cd-2fada8f345b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7a02-96cd-2fada8f345b2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7a02-96cd-2fada8f345b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7478-b743-d5f6d38b4935" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7097-7a02-96cd-2fada8f345b2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7478-b743-d5f6d38b4935" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-7097-73be-8edc-a7a6b36d2a3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7097-7478-b743-d5f6d38b4935" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-7097-73be-8edc-a7a6b36d2a3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-7097-7837-a4b4-e7987d103e24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-7097-7837-a4b4-e7987d103e24" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7837-a4b4-e7987d103e24_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-7097-7837-a4b4-e7987d103e24" xlink:to="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7837-a4b4-e7987d103e24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7f65-ac0b-12e0ddaf9aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019dd587-7097-7837-a4b4-e7987d103e24" xlink:to="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7f65-ac0b-12e0ddaf9aa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019dd587-7097-7cb7-b46d-57c17a122eea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7f65-ac0b-12e0ddaf9aa4" xlink:to="loc_us-gaap_NonrelatedPartyMember_019dd587-7097-7cb7-b46d-57c17a122eea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-7097-7b50-854b-f92a9cef5d37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019dd587-7097-7f65-ac0b-12e0ddaf9aa4" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-7097-7b50-854b-f92a9cef5d37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-7097-733e-bff6-cbb540c6ab45" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_srt_StatementScenarioAxis_019dd587-7097-733e-bff6-cbb540c6ab45" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-733e-bff6-cbb540c6ab45_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7097-733e-bff6-cbb540c6ab45" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-733e-bff6-cbb540c6ab45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7f32-8a03-0d51ee40817b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7097-733e-bff6-cbb540c6ab45" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7f32-8a03-0d51ee40817b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-7097-7fdc-a1cd-111b545c4eb2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7f32-8a03-0d51ee40817b" xlink:to="loc_srt_ScenarioForecastMember_019dd587-7097-7fdc-a1cd-111b545c4eb2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dd587-7097-74c4-bb1e-85af410cbade" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_dei_LegalEntityAxis_019dd587-7097-74c4-bb1e-85af410cbade" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-7097-74c4-bb1e-85af410cbade_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dd587-7097-74c4-bb1e-85af410cbade" xlink:to="loc_dei_EntityDomain_019dd587-7097-74c4-bb1e-85af410cbade_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dd587-7097-75ff-8028-95ba52d93bb1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dd587-7097-74c4-bb1e-85af410cbade" xlink:to="loc_dei_EntityDomain_019dd587-7097-75ff-8028-95ba52d93bb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsMember_019dd587-7097-74a1-b782-0af4b6f37e00" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-7097-75ff-8028-95ba52d93bb1" xlink:to="loc_dpl_OhioHoldingsMember_019dd587-7097-74a1-b782-0af4b6f37e00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsMember_019dd587-7097-7992-98c9-c09899cae242" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dd587-7097-75ff-8028-95ba52d93bb1" xlink:to="loc_dpl_OhioInvestmentsMember_019dd587-7097-7992-98c9-c09899cae242" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019dd587-7097-7755-b6c9-13465724c616" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dpl_SignificantAccountingPoliciesTable_019dd587-7097-7801-b8b3-00e470810c37" xlink:to="loc_srt_OwnershipAxis_019dd587-7097-7755-b6c9-13465724c616" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-7097-7755-b6c9-13465724c616_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019dd587-7097-7755-b6c9-13465724c616" xlink:to="loc_srt_OwnershipDomain_019dd587-7097-7755-b6c9-13465724c616_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dd587-7097-70ae-a852-152666069cb2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019dd587-7097-7755-b6c9-13465724c616" xlink:to="loc_srt_OwnershipDomain_019dd587-7097-70ae-a852-152666069cb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsMember_019dd587-7097-7ab3-81ab-d8052f087d53" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-7097-70ae-a852-152666069cb2" xlink:to="loc_dpl_OhioHoldingsMember_019dd587-7097-7ab3-81ab-d8052f087d53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsMember_019dd587-7097-7025-8fdf-5f6d463bf36b" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-7097-70ae-a852-152666069cb2" xlink:to="loc_dpl_OhioInvestmentsMember_019dd587-7097-7025-8fdf-5f6d463bf36b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLMember_019dd587-7097-74d7-8155-1b3112db64d1" xlink:href="dpl-20260331.xsd#dpl_DPLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dd587-7097-70ae-a852-152666069cb2" xlink:to="loc_dpl_DPLMember_019dd587-7097-74d7-8155-1b3112db64d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019dd587-7097-7f2d-a7c1-27fb3d5372b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_NumberOfReportableSegments_019dd587-7097-7f2d-a7c1-27fb3d5372b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-7fb5-b8a9-b6f4e28883df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019dd587-7097-7fb5-b8a9-b6f4e28883df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCash_019dd587-7097-7721-ae8d-db83222c0b47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_RestrictedCash_019dd587-7097-7721-ae8d-db83222c0b47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_019dd587-7097-7dce-b33d-a7b76215bcda" xlink:href="dpl-20260331.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_NumberOfRetailCustomers_019dd587-7097-7dce-b33d-a7b76215bcda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_019dd587-7097-70ff-907c-2b1d77728e36" xlink:href="dpl-20260331.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_ServiceAreaSquareMiles_019dd587-7097-70ff-907c-2b1d77728e36" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019dd587-7097-7b17-8350-b795e0d11009" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019dd587-7097-7b17-8350-b795e0d11009" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExciseTaxesCollected_019dd587-7097-774c-a8bc-b674768f097a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExciseTaxesCollected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ExciseTaxesCollected_019dd587-7097-774c-a8bc-b674768f097a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CustomerReceivables_019dd587-7097-7fb8-a050-646029785c8d" xlink:href="dpl-20260331.xsd#dpl_CustomerReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_CustomerReceivables_019dd587-7097-7fb8-a050-646029785c8d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UnbilledRevenue_019dd587-7097-7377-a634-e4e7cc98677c" xlink:href="dpl-20260331.xsd#dpl_UnbilledRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_UnbilledRevenue_019dd587-7097-7377-a634-e4e7cc98677c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DuefromPJMtransmissionsettlement_019dd587-7097-7521-ac84-eb7c1ae4b027" xlink:href="dpl-20260331.xsd#dpl_DuefromPJMtransmissionsettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_DuefromPJMtransmissionsettlement_019dd587-7097-7521-ac84-eb7c1ae4b027" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivables_019dd587-7097-73cb-899e-bb5d73665481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherReceivables_019dd587-7097-73cb-899e-bb5d73665481" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-76ef-b76e-28a4db796900" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_019dd587-7097-76ef-b76e-28a4db796900" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-78e0-a850-ebbd8e7a5702" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019dd587-7097-78e0-a850-ebbd8e7a5702" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_019dd587-7097-7983-bcbe-719ce32b2692" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_019dd587-7097-7983-bcbe-719ce32b2692" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_019dd587-7097-7b65-98f2-0e0602b6c5cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs_019dd587-7097-7b65-98f2-0e0602b6c5cb" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_019dd587-7097-7592-9f67-7abd8a50979c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRecoveries_019dd587-7097-7592-9f67-7abd8a50979c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-7097-710b-9b2f-572ac5cd0241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-7097-710b-9b2f-572ac5cd0241" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-7097-7853-b1aa-ecc81c4da46e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-7097-7853-b1aa-ecc81c4da46e" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019dd587-7097-7f70-92c7-8b1670941505" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ProfitLoss_019dd587-7097-7f70-92c7-8b1670941505" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019dd587-7097-7ae8-855c-541facdb5cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019dd587-7097-7ae8-855c-541facdb5cb6" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-735b-b59c-aa138ee032dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7097-735b-b59c-aa138ee032dc" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7673-9ebd-b0b728a0aa51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019dd587-7097-7673-9ebd-b0b728a0aa51" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019dd587-7097-76cc-88e6-d6bc406e66bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019dd587-7097-76cc-88e6-d6bc406e66bd" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-7897-8dce-cd2236b5d03f" 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_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7097-7897-8dce-cd2236b5d03f" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-7097-7993-939c-e3ea2ec957b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-7097-7993-939c-e3ea2ec957b6" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-7097-70ec-b3ea-45b2fc7ff4fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-7097-70ec-b3ea-45b2fc7ff4fc" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-7097-7297-ad9b-b6004875d75f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019dd587-7097-7297-ad9b-b6004875d75f" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-7d83-8758-d4d2ba399fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019dd587-7097-7d83-8758-d4d2ba399fa2" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-7842-8a66-6ae9a70ab5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019dd587-7097-7842-8a66-6ae9a70ab5a3" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-7097-746a-afc0-86bb67a20697" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax_019dd587-7097-746a-afc0-86bb67a20697" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-7097-793c-a7f8-788f27de96a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019dd587-7097-793c-a7f8-788f27de96a0" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_019dd587-7097-70f3-b044-4c62a026728a" xlink:href="dpl-20260331.xsd#dpl_AllowanceForFundsUsedDuringConstructionEquityPortion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_AllowanceForFundsUsedDuringConstructionEquityPortion_019dd587-7097-70f3-b044-4c62a026728a" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalizedAdjustment_019dd587-7097-73b3-8936-f68aa588b1d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalizedAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_InterestCostsCapitalizedAdjustment_019dd587-7097-73b3-8936-f68aa588b1d4" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalized_019dd587-7097-7272-aa09-cf9dc7a80caa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_InterestCostsCapitalized_019dd587-7097-7272-aa09-cf9dc7a80caa" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_019dd587-7097-7312-a8ea-f3b6fea687b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest_019dd587-7097-7312-a8ea-f3b6fea687b9" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-7097-7812-9b99-e3695d9df482" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-7097-7812-9b99-e3695d9df482" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsPurchasePrice_019dd587-7097-761d-9438-37f2f897250d" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_OhioHoldingsPurchasePrice_019dd587-7097-761d-9438-37f2f897250d" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentsPurchasePrice_019dd587-7097-78f6-9557-9d9c9ad1acd5" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentsPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_OhioInvestmentsPurchasePrice_019dd587-7097-78f6-9557-9d9c9ad1acd5" xlink:type="arc" order="37"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentTotal_019dd587-7097-7300-a9f3-c9a48f00da56" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_CDPQInvestmentTotal_019dd587-7097-7300-a9f3-c9a48f00da56" xlink:type="arc" order="38"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioHoldingsInvestmentPercent_019dd587-7097-7515-9b68-dd0c3e0d3c16" xlink:href="dpl-20260331.xsd#dpl_OhioHoldingsInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_OhioHoldingsInvestmentPercent_019dd587-7097-7515-9b68-dd0c3e0d3c16" xlink:type="arc" order="39"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OhioInvestmentPercent_019dd587-7097-7116-b142-11f1696deec9" xlink:href="dpl-20260331.xsd#dpl_OhioInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_OhioInvestmentPercent_019dd587-7097-7116-b142-11f1696deec9" xlink:type="arc" order="40"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CDPQInvestmentPercent_019dd587-7097-78b2-8425-f167bc4338f3" xlink:href="dpl-20260331.xsd#dpl_CDPQInvestmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_dpl_CDPQInvestmentPercent_019dd587-7097-78b2-8425-f167bc4338f3" xlink:type="arc" order="41"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-7097-7210-be0c-df5e20df60a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_SignificantAccountingPoliciesLineItems_019dd587-7097-72b6-beca-48e68070b015" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019dd587-7097-7210-be0c-df5e20df60a8" xlink:type="arc" order="42"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-7097-7f67-b40f-a51d3a31a454" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019dd587-7097-729b-ad89-efbc71ff49d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-7097-7f67-b40f-a51d3a31a454" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019dd587-7097-729b-ad89-efbc71ff49d3" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7bb0-b1f6-6163ae832820" 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_019dd587-7097-729b-ad89-efbc71ff49d3" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7bb0-b1f6-6163ae832820" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7bb0-b1f6-6163ae832820_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7c66-b822-a86b95570e27" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-7e8e-9915-e88e6728478f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7ecd-be23-102e037f0be1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-7097-7f67-b40f-a51d3a31a454" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019dd587-7097-7ecd-be23-102e037f0be1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PropertyPlantAndEquipmentNetOfDepreciation_019dd587-7097-7fb1-acb6-08c1bec9c14c" xlink:href="dpl-20260331.xsd#dpl_PropertyPlantAndEquipmentNetOfDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-7097-7f67-b40f-a51d3a31a454" xlink:to="loc_dpl_PropertyPlantAndEquipmentNetOfDepreciation_019dd587-7097-7fb1-acb6-08c1bec9c14c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-7097-72d4-a902-c8843e82112f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019dd587-7097-7f67-b40f-a51d3a31a454" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019dd587-7097-72d4-a902-c8843e82112f" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RegulatoryMattersDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RegulatoryMattersDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RegulatoryMattersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7097-749e-80dd-3468ebc45b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_us-gaap_StatementTable_019dd587-7097-749e-80dd-3468ebc45b7e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetAxis_019dd587-7097-7063-b0f1-d5dcd75bae93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-749e-80dd-3468ebc45b7e" xlink:to="loc_us-gaap_RegulatoryAssetAxis_019dd587-7097-7063-b0f1-d5dcd75bae93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7063-b0f1-d5dcd75bae93_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegulatoryAssetAxis_019dd587-7097-7063-b0f1-d5dcd75bae93" xlink:to="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7063-b0f1-d5dcd75bae93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7d0b-a31c-37eb3bb486b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegulatoryAssetAxis_019dd587-7097-7063-b0f1-d5dcd75bae93" xlink:to="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7d0b-a31c-37eb3bb486b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UnrecoveredOVECChargesMember_019dd587-7097-7afe-af20-86c45a5fc560" xlink:href="dpl-20260331.xsd#dpl_UnrecoveredOVECChargesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7d0b-a31c-37eb3bb486b4" xlink:to="loc_dpl_UnrecoveredOVECChargesMember_019dd587-7097-7afe-af20-86c45a5fc560" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_COVID19DeferralMember_019dd587-7097-77b4-8b08-54f259dc1081" xlink:href="dpl-20260331.xsd#dpl_COVID19DeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegulatoryAssetDomain_019dd587-7097-7d0b-a31c-37eb3bb486b4" xlink:to="loc_dpl_COVID19DeferralMember_019dd587-7097-77b4-8b08-54f259dc1081" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7097-733c-b2b4-60bcb0ac2ff4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7097-749e-80dd-3468ebc45b7e" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7097-733c-b2b4-60bcb0ac2ff4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7097-733c-b2b4-60bcb0ac2ff4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7097-733c-b2b4-60bcb0ac2ff4" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7097-733c-b2b4-60bcb0ac2ff4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7097-7681-9c7d-e56ab8782ce7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7097-733c-b2b4-60bcb0ac2ff4" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7097-7681-9c7d-e56ab8782ce7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-7097-75d3-8f1c-ccdb36610b28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7097-7681-9c7d-e56ab8782ce7" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-7097-75d3-8f1c-ccdb36610b28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DistributionInvestmentRider_019dd587-7097-7624-9e90-3ba1efccc628" xlink:href="dpl-20260331.xsd#dpl_DistributionInvestmentRider"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_DistributionInvestmentRider_019dd587-7097-7624-9e90-3ba1efccc628" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-7087-b6a7-2c3550f3577f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_019dd587-7097-7087-b6a7-2c3550f3577f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-7097-758c-b505-24aee86b39e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsAndLiabilitiesTextBlock_019dd587-7097-758c-b505-24aee86b39e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Covid19DeferralWriteOff_019dd587-7097-785f-a52b-abe76ff07933" xlink:href="dpl-20260331.xsd#dpl_Covid19DeferralWriteOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_Covid19DeferralWriteOff_019dd587-7097-785f-a52b-abe76ff07933" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-7097-70b8-b0ad-a476d1970091" xlink:href="dpl-20260331.xsd#dpl_CostOfLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-7097-70b8-b0ad-a476d1970091" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-7097-76fc-9bf9-b2ab65ec32b4" xlink:href="dpl-20260331.xsd#dpl_RevenueIncreaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-7097-76fc-9bf9-b2ab65ec32b4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-7097-7304-8515-b54451cab998" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-7097-7304-8515-b54451cab998" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseDistributionRateCase_019dd587-7097-7b7a-bbe5-cc6fb537512e" xlink:href="dpl-20260331.xsd#dpl_RateBaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_RateBaseDistributionRateCase_019dd587-7097-7b7a-bbe5-cc6fb537512e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-7097-7418-892a-9d2048cbdd0b" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-7097-7418-892a-9d2048cbdd0b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-7097-7e0d-bc16-3ed3ca167346" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-7097-7e0d-bc16-3ed3ca167346" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityESP4_019dd587-7097-7f5f-a019-d07a33e4c035" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_ReturnOnEquityESP4_019dd587-7097-7f5f-a019-d07a33e4c035" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RecoveryESP4_019dd587-7097-7244-9e3e-aeec79201a65" xlink:href="dpl-20260331.xsd#dpl_RecoveryESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_RecoveryESP4_019dd587-7097-7244-9e3e-aeec79201a65" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferralOfPurchasedPowerCostsESP4_019dd587-7097-7d3d-b36a-c60235d881ae" xlink:href="dpl-20260331.xsd#dpl_DeferralOfPurchasedPowerCostsESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_DeferralOfPurchasedPowerCostsESP4_019dd587-7097-7d3d-b36a-c60235d881ae" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferralOfCarryingCostsESP4_019dd587-7097-70eb-8a4b-f55b947ea3d7" xlink:href="dpl-20260331.xsd#dpl_DeferralOfCarryingCostsESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7d72-a76a-e787977394d3" xlink:to="loc_dpl_DeferralOfCarryingCostsESP4_019dd587-7097-70eb-8a4b-f55b947ea3d7" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-7097-7f1d-832e-7c3930bb444c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-7097-7f1d-832e-7c3930bb444c" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7498-8519-cfcfab464a15" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-7097-7f1d-832e-7c3930bb444c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7498-8519-cfcfab464a15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7498-8519-cfcfab464a15_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7498-8519-cfcfab464a15" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7498-8519-cfcfab464a15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7fe4-8c04-7b9fad1d6556" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-7498-8519-cfcfab464a15" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7fe4-8c04-7b9fad1d6556" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-738f-ae0d-841424cad86b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7fe4-8c04-7b9fad1d6556" xlink:to="loc_srt_SubsidiariesMember_019dd587-7097-738f-ae0d-841424cad86b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-7097-7fee-9aff-a9c1c13c8a94" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_019dd587-7097-7f1d-832e-7c3930bb444c" xlink:to="loc_srt_StatementScenarioAxis_019dd587-7097-7fee-9aff-a9c1c13c8a94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7fee-9aff-a9c1c13c8a94_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7097-7fee-9aff-a9c1c13c8a94" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7fee-9aff-a9c1c13c8a94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7db4-ae4b-3cc16a8f8f6c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7097-7fee-9aff-a9c1c13c8a94" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7db4-ae4b-3cc16a8f8f6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-7097-71c7-bc49-036f78e01b78" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-7097-7db4-ae4b-3cc16a8f8f6c" xlink:to="loc_srt_ScenarioForecastMember_019dd587-7097-71c7-bc49-036f78e01b78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-7097-7f67-b221-25cc7525d8f0" xlink:href="dpl-20260331.xsd#dpl_RevenueIncreaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_RevenueIncreaseDistributionRateCase_019dd587-7097-7f67-b221-25cc7525d8f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-7097-7f6e-a0bd-e69551c1cd00" xlink:href="dpl-20260331.xsd#dpl_ReturnOnEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_ReturnOnEquityDistributionRateCase_019dd587-7097-7f6e-a0bd-e69551c1cd00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-7097-71ba-b748-584ee882fbe7" xlink:href="dpl-20260331.xsd#dpl_CostOfLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_CostOfLongTermDebtDistributionRateCase_019dd587-7097-71ba-b748-584ee882fbe7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RateBaseDistributionRateCase_019dd587-7097-7292-8c27-087c6ec4f4c3" xlink:href="dpl-20260331.xsd#dpl_RateBaseDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_RateBaseDistributionRateCase_019dd587-7097-7292-8c27-087c6ec4f4c3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-7097-79ce-8d4a-b16242a76753" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureEquityDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_CapitalStructureEquityDistributionRateCase_019dd587-7097-79ce-8d4a-b16242a76753" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-7097-7e3a-bca5-1e07801c58c4" xlink:href="dpl-20260331.xsd#dpl_CapitalStructureLongTermDebtDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_CapitalStructureLongTermDebtDistributionRateCase_019dd587-7097-7e3a-bca5-1e07801c58c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TFRTrueUpLiability_019dd587-7097-7077-a1c4-c56d32f5896b" xlink:href="dpl-20260331.xsd#dpl_TFRTrueUpLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_TFRTrueUpLiability_019dd587-7097-7077-a1c4-c56d32f5896b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TFRTrueUpLiabilityCurrent_019dd587-7097-744d-a76e-ee562abeff76" xlink:href="dpl-20260331.xsd#dpl_TFRTrueUpLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_TFRTrueUpLiabilityCurrent_019dd587-7097-744d-a76e-ee562abeff76" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RSCRider_019dd587-7097-76dd-afe7-0567485f3125" xlink:href="dpl-20260331.xsd#dpl_RSCRider"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_RSCRider_019dd587-7097-76dd-afe7-0567485f3125" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RecoveryESP4_019dd587-7097-7991-943f-c0c9ce7dff9c" xlink:href="dpl-20260331.xsd#dpl_RecoveryESP4"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_RecoveryESP4_019dd587-7097-7991-943f-c0c9ce7dff9c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2Costs_019dd587-7097-74e7-9428-ac5a63cccbc5" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2Costs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_EstimatedSmartGridPhase2Costs_019dd587-7097-74e7-9428-ac5a63cccbc5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2Capital_019dd587-7097-7c92-a908-6782f20d52fa" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2Capital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_EstimatedSmartGridPhase2Capital_019dd587-7097-7c92-a908-6782f20d52fa" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedSmartGridPhase2OM_019dd587-7097-7eb6-a970-484ac9578957" xlink:href="dpl-20260331.xsd#dpl_EstimatedSmartGridPhase2OM"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_EstimatedSmartGridPhase2OM_019dd587-7097-7eb6-a970-484ac9578957" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryLiabilities_019dd587-7097-7d55-8e07-c0bfb82d9ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RegulatoryLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_us-gaap_RegulatoryLiabilities_019dd587-7097-7d55-8e07-c0bfb82d9ab2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NetCostDeferralDistributionRateCase_019dd587-7097-74db-9d9f-aac6d88b7517" xlink:href="dpl-20260331.xsd#dpl_NetCostDeferralDistributionRateCase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_019dd587-7097-7600-ab2d-a53d3176d132" xlink:to="loc_dpl_NetCostDeferralDistributionRateCase_019dd587-7097-74db-9d9f-aac6d88b7517" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-7097-7115-b703-cf87fe90b13a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-7097-7115-b703-cf87fe90b13a" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-73a9-adad-a7d228212e75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-73a9-adad-a7d228212e75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-73a9-adad-a7d228212e75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-73a9-adad-a7d228212e75" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-73a9-adad-a7d228212e75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7435-a0dc-f8de2c546732" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-73a9-adad-a7d228212e75" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7435-a0dc-f8de2c546732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-79be-9208-92cf87173f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7435-a0dc-f8de2c546732" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-79be-9208-92cf87173f0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-7201-aed1-309d9ef82b9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7435-a0dc-f8de2c546732" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-7201-aed1-309d9ef82b9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-732f-a7a4-edaae5812740" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-732f-a7a4-edaae5812740" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-732f-a7a4-edaae5812740_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-732f-a7a4-edaae5812740" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-732f-a7a4-edaae5812740_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-77f9-bdab-ec4d86661adc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-732f-a7a4-edaae5812740" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-77f9-bdab-ec4d86661adc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dd587-7097-7dba-b04a-1160b5ef85a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-77f9-bdab-ec4d86661adc" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dd587-7097-7dba-b04a-1160b5ef85a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dd587-7097-7b8f-ab05-7786145267ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-77f9-bdab-ec4d86661adc" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dd587-7097-7b8f-ab05-7786145267ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-7097-7055-801a-18bf5a47f8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-77f9-bdab-ec4d86661adc" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-7097-7055-801a-18bf5a47f8e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-75af-9118-bda0e532df2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-75af-9118-bda0e532df2c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-75af-9118-bda0e532df2c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-75af-9118-bda0e532df2c" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-75af-9118-bda0e532df2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-75af-9118-bda0e532df2c" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7ea6-be67-c6420a49382e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7ea6-be67-c6420a49382e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7b68-a0ba-3b12183a347e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7b68-a0ba-3b12183a347e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-7c48-9444-7ce967626b2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-7c48-9444-7ce967626b2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-7097-71b4-9757-2d7b3e762c00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-734e-bab1-4f175290eb65" xlink:to="loc_us-gaap_DebtMember_019dd587-7097-71b4-9757-2d7b3e762c00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-703d-9344-d3d57cb7d671" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-77ff-a465-dc3832695cd6" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-703d-9344-d3d57cb7d671" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-703d-9344-d3d57cb7d671_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-703d-9344-d3d57cb7d671" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-703d-9344-d3d57cb7d671_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7c86-960f-92e2fa6542c2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7097-703d-9344-d3d57cb7d671" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7c86-960f-92e2fa6542c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7097-784d-9895-faa844886d8d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7097-7c86-960f-92e2fa6542c2" xlink:to="loc_srt_SubsidiariesMember_019dd587-7097-784d-9895-faa844886d8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7097-78ca-b52b-4eb0869850d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-7097-7115-b703-cf87fe90b13a" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7097-78ca-b52b-4eb0869850d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-7097-7172-81d2-8a3264ecf1ed" xlink:href="dpl-20260331.xsd#dpl_InvestmentsOtherThanDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-7097-7115-b703-cf87fe90b13a" xlink:to="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-7097-7172-81d2-8a3264ecf1ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-7097-7dc0-8ac6-e61f3b515b40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019dd587-7097-7115-b703-cf87fe90b13a" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019dd587-7097-7dc0-8ac6-e61f3b515b40" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueandCostofNonDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueFairValueandCostofNonDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueFairValueandCostofNonDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7097-7afa-beaf-e2d9f8b8f677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-7a2f-9167-1241c61b0529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7afa-beaf-e2d9f8b8f677" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-7a2f-9167-1241c61b0529" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7f5a-a851-c752c12ab420" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-7a2f-9167-1241c61b0529" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7f5a-a851-c752c12ab420" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f5a-a851-c752c12ab420_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7f5a-a851-c752c12ab420" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f5a-a851-c752c12ab420_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7f5a-a851-c752c12ab420" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7484-bac8-a43b4b082102" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7484-bac8-a43b4b082102" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7d41-a552-86c83bc679b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7d41-a552-86c83bc679b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-704d-991f-7e67be81f4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-704d-991f-7e67be81f4ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-7097-7ee1-8022-38f1e375b74d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7f01-8958-33f0a61ff589" xlink:to="loc_us-gaap_DebtMember_019dd587-7097-7ee1-8022-38f1e375b74d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-7595-9ec0-c71f39943cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-7a2f-9167-1241c61b0529" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-7595-9ec0-c71f39943cee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7595-9ec0-c71f39943cee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-7595-9ec0-c71f39943cee" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7595-9ec0-c71f39943cee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7e39-97ca-7f16188f80af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-7595-9ec0-c71f39943cee" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7e39-97ca-7f16188f80af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7410-a1ab-5548cf49847c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7e39-97ca-7f16188f80af" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7410-a1ab-5548cf49847c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dd587-7097-7826-a111-d6e1045e34f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7e39-97ca-7f16188f80af" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019dd587-7097-7826-a111-d6e1045e34f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7f11-86b7-2fcc7d34765f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-71ef-8124-b9ece750d015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7f71-ad8a-6276783d65e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-7e3d-8f03-c0bb2fa6ebbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7e39-97ca-7f16188f80af" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-7e3d-8f03-c0bb2fa6ebbc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-7097-7fd8-abf8-8a464ae82442" xlink:href="dpl-20260331.xsd#dpl_InvestmentsOtherThanDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7afa-beaf-e2d9f8b8f677" xlink:to="loc_dpl_InvestmentsOtherThanDerivatives_019dd587-7097-7fd8-abf8-8a464ae82442" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-7097-7b77-841d-543916eda584" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7afa-beaf-e2d9f8b8f677" xlink:to="loc_us-gaap_LongTermDebt_019dd587-7097-7b77-841d-543916eda584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7097-7bd1-8466-8d50ac030b27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7097-7afa-beaf-e2d9f8b8f677" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7097-7bd1-8466-8d50ac030b27" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueFairValueofAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7966-91fa-b195a7539152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7966-91fa-b195a7539152" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7966-91fa-b195a7539152_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7966-91fa-b195a7539152" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7966-91fa-b195a7539152_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019dd587-7097-7966-91fa-b195a7539152" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7b21-a634-41effa9e5f1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019dd587-7097-7b21-a634-41effa9e5f1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7625-b07e-9153b0528533" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_EquitySecuritiesMember_019dd587-7097-7625-b07e-9153b0528533" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-75d9-a8d6-115994df1530" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_DebtSecuritiesMember_019dd587-7097-75d9-a8d6-115994df1530" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtMember_019dd587-7097-7fbe-99ae-192e7fac0873" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_DebtMember_019dd587-7097-7fbe-99ae-192e7fac0873" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_019dd587-7097-77bf-a69b-ad2870794559" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_MutualFundMember_019dd587-7097-77bf-a69b-ad2870794559" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019dd9ce-472e-7523-b9b6-94c9918c18c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019dd587-7097-7323-a255-4973d3c9d0bd" xlink:to="loc_us-gaap_LineOfCreditMember_019dd9ce-472e-7523-b9b6-94c9918c18c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-70a8-8eff-19477d91db23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-70a8-8eff-19477d91db23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-70a8-8eff-19477d91db23_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-70a8-8eff-19477d91db23" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-70a8-8eff-19477d91db23_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7b9e-ad8f-fc023e23197a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019dd587-7097-70a8-8eff-19477d91db23" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7b9e-ad8f-fc023e23197a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7aab-bbb5-c568fdc9cc11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019dd587-7097-7b9e-ad8f-fc023e23197a" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7aab-bbb5-c568fdc9cc11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-71b6-982b-580cbc9cee9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019dd587-7097-7aab-bbb5-c568fdc9cc11" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019dd587-7097-71b6-982b-580cbc9cee9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-7d84-a3f6-765d1ce27386" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-7d84-a3f6-765d1ce27386" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-7d84-a3f6-765d1ce27386_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-7d84-a3f6-765d1ce27386" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7097-7d84-a3f6-765d1ce27386_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7098-7a52-974a-f0cec1472d32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-7097-7d84-a3f6-765d1ce27386" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7098-7a52-974a-f0cec1472d32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019dd587-7098-7517-91a4-556370ff5df7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7098-7a52-974a-f0cec1472d32" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019dd587-7098-7517-91a4-556370ff5df7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019dd587-7098-7277-a9e4-8ef0c8a1bfd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7098-7a52-974a-f0cec1472d32" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019dd587-7098-7277-a9e4-8ef0c8a1bfd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-7098-70d7-a358-c58ab968eed3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-7098-7a52-974a-f0cec1472d32" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-7098-70d7-a358-c58ab968eed3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7098-70c3-82a1-1f25f331e013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019dd587-7097-704a-b486-c7aeec15fea8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7098-70c3-82a1-1f25f331e013" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7098-70c3-82a1-1f25f331e013_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7098-70c3-82a1-1f25f331e013" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7098-70c3-82a1-1f25f331e013_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7098-730b-a081-50fd4b5257a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dd587-7098-70c3-82a1-1f25f331e013" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7098-730b-a081-50fd4b5257a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019dd587-7098-7626-9743-197d7a5b0dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dd587-7098-730b-a081-50fd4b5257a0" xlink:to="loc_us-gaap_InterestRateContractMember_019dd587-7098-7626-9743-197d7a5b0dc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019dd587-7098-7ec7-9ddd-2d2bc9f3c030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019dd587-7098-7ec7-9ddd-2d2bc9f3c030" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7098-793e-8eb2-1fe10901bea3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019dd587-7098-793e-8eb2-1fe10901bea3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019dd587-7098-7343-b332-42b127d356a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019dd587-7098-7343-b332-42b127d356a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-7098-7a22-9eaf-ca640b8bb291" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_LongTermDebt_019dd587-7098-7a22-9eaf-ca640b8bb291" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dd9d0-44c9-7cd3-8e3f-3a536fda2c19" 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_019dd587-7098-7f7e-b8f3-fa12406498dd" xlink:to="loc_us-gaap_LineOfCredit_019dd9d0-44c9-7cd3-8e3f-3a536fda2c19" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FairValueCashEquivalentsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FairValueCashEquivalentsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FairValueCashEquivalentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7098-7b3d-abeb-a95d795f3f8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7098-777e-ab37-3dd4ee7d34f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7b3d-abeb-a95d795f3f8a" xlink:to="loc_us-gaap_StatementTable_019dd587-7098-777e-ab37-3dd4ee7d34f3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7bbc-bcec-d89f25361a25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7bbc-bcec-d89f25361a25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-70f6-892b-c8daa36320ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7bbc-bcec-d89f25361a25" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-70f6-892b-c8daa36320ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-70f6-892b-c8daa36320ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-70f6-892b-c8daa36320ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-70f6-892b-c8daa36320ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-70f6-892b-c8daa36320ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-7098-70b6-a45b-6ddd3203fa0d" xlink:href="dpl-20260331.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-7098-70b6-a45b-6ddd3203fa0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-7098-701a-86a5-39bc9a7450ae" xlink:href="dpl-20260331.xsd#dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-7098-701a-86a5-39bc9a7450ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-7098-737a-b28f-8d4b96aad372" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dd587-7098-737a-b28f-8d4b96aad372" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-7098-7292-b30b-c2f022780dcf" xlink:href="dpl-20260331.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-7098-7292-b30b-c2f022780dcf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-7098-79c9-a611-761b01776f77" xlink:href="dpl-20260331.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-7098-79c9-a611-761b01776f77" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-70fa-87c5-4f3d9b50eb23" xlink:href="dpl-20260331.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-70fa-87c5-4f3d9b50eb23" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-79be-b074-b9bd0804c35e" xlink:href="dpl-20260331.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-79be-b074-b9bd0804c35e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-7681-a3cb-b56c62ba38d9" xlink:href="dpl-20260331.xsd#dpl_TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-7681-a3cb-b56c62ba38d9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FirstMortgageBondsDue2033Member_019dd587-7098-7c22-b915-bb060cec55c0" xlink:href="dpl-20260331.xsd#dpl_FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_FirstMortgageBondsDue2033Member_019dd587-7098-7c22-b915-bb060cec55c0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-7098-79c5-af32-f1119ad784ea" xlink:href="dpl-20260331.xsd#dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-7098-79c5-af32-f1119ad784ea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-7098-73f1-b6c3-e9f78b0849cc" xlink:href="dpl-20260331.xsd#dpl_A5.49SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-7098-73f1-b6c3-e9f78b0849cc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.55FirstMortgageBondDue2030Member_019dd587-7098-7fdc-90dd-7c1093026dfb" xlink:href="dpl-20260331.xsd#dpl_A4.55FirstMortgageBondDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A4.55FirstMortgageBondDue2030Member_019dd587-7098-7fdc-90dd-7c1093026dfb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-7098-75aa-b049-a431ea584944" xlink:href="dpl-20260331.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-7098-75aa-b049-a431ea584944" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-7098-786e-96e7-ce4f779c0f08" xlink:href="dpl-20260331.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-716f-99da-58b96d6b5111" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-7098-786e-96e7-ce4f779c0f08" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-7098-7135-bb14-d13337f48c02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7bbc-bcec-d89f25361a25" xlink:to="loc_srt_StatementScenarioAxis_019dd587-7098-7135-bb14-d13337f48c02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7135-bb14-d13337f48c02_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7135-bb14-d13337f48c02" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7135-bb14-d13337f48c02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-723c-88bc-5792d05673c2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7135-bb14-d13337f48c02" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-723c-88bc-5792d05673c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-7098-7978-9e5e-1a03987d3506" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-723c-88bc-5792d05673c2" xlink:to="loc_srt_ScenarioForecastMember_019dd587-7098-7978-9e5e-1a03987d3506" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7f94-b2de-f071f779ebd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-7098-7bbc-bcec-d89f25361a25" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7f94-b2de-f071f779ebd7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7f94-b2de-f071f779ebd7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7f94-b2de-f071f779ebd7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7f94-b2de-f071f779ebd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7b65-abf8-43aa02f0d952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7f94-b2de-f071f779ebd7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7b65-abf8-43aa02f0d952" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-7098-7070-a039-0cf082529dd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7b65-abf8-43aa02f0d952" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-7098-7070-a039-0cf082529dd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dd587-7098-707e-81cb-cf48751a4af8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_LineOfCredit_019dd587-7098-707e-81cb-cf48751a4af8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-7098-76d0-895a-cc927c73094d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-7098-76d0-895a-cc927c73094d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentNumberofFinancialCovenants_019dd587-7098-7766-b47d-778e14a34f57" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentNumberofFinancialCovenants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentNumberofFinancialCovenants_019dd587-7098-7766-b47d-778e14a34f57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters_019dd587-7098-785a-b546-5529353b1b72" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAtoInterestCalculationNumberofQuarters_019dd587-7098-785a-b546-5529353b1b72" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantDebttoEBITDARatioMaximum_019dd587-7098-7edf-bf8a-7921efe2fdc7" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantDebttoEBITDARatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtCovenantDebttoEBITDARatioMaximum_019dd587-7098-7edf-bf8a-7921efe2fdc7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantLeverageRatioMaximum_019dd587-7098-74ab-bb28-607759cb4a02" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtCovenantLeverageRatioMaximum_019dd587-7098-74ab-bb28-607759cb4a02" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-7098-73ab-869f-c48bec659eff" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantInterestCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-7098-73ab-869f-c48bec659eff" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-7098-7e52-adbf-d679b22440bd" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-7098-7e52-adbf-d679b22440bd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7098-7580-9404-a7c5c2a040a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7098-7580-9404-a7c5c2a040a4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-7098-7e56-93ef-0cba7baeecd6" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-7098-7e56-93ef-0cba7baeecd6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-7098-7041-9d81-b3673911c901" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-7098-7041-9d81-b3673911c901" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-7098-73d5-aa84-8fab3a051ee4" xlink:href="dpl-20260331.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-7098-73d5-aa84-8fab3a051ee4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-7098-7068-bfac-28da7244ed66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet_019dd587-7098-7068-bfac-28da7244ed66" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-7098-7a20-814d-00c0b31d60f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_LongTermDebt_019dd587-7098-7a20-814d-00c0b31d60f5" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit_019dd587-7098-78ac-bc5d-13b313579281" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDACurrentBorrowingLimit_019dd587-7098-78ac-bc5d-13b313579281" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit_019dd587-7098-71e0-aa68-862b481c3639" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAMaximumBorrowingLimit_019dd587-7098-71e0-aa68-862b481c3639" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction_019dd587-7098-7f5e-b564-2fe67b48aeb8" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtInstrumentDebtCovenantTotalDebtToEBITDAQuarterlyBorrowingLimitReduction_019dd587-7098-7f5e-b564-2fe67b48aeb8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-7098-75fc-bbe7-494bdd53c7f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-7098-75fc-bbe7-494bdd53c7f1" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBankLoansAndNotesPayable_019dd587-7098-7bc1-ba80-d76c4edb04c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBankLoansAndNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_ShortTermBankLoansAndNotesPayable_019dd587-7098-7bc1-ba80-d76c4edb04c9" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dd587-7098-7ecd-a370-69ce5a3f1a70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dd587-7098-7ecd-a370-69ce5a3f1a70" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UncommittedAccordionFeature_019dd587-7098-7be4-90fb-4526e927568d" xlink:href="dpl-20260331.xsd#dpl_UncommittedAccordionFeature"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_UncommittedAccordionFeature_019dd587-7098-7be4-90fb-4526e927568d" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019dd587-7098-7ae0-8279-094682dba43d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_LongTermDebtCurrent_019dd587-7098-7ae0-8279-094682dba43d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7098-7b3d-8cdc-f1fb006efaeb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7098-7b3d-8cdc-f1fb006efaeb" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-7098-7a81-9ef7-e24de204ab78" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-7e13-afba-902cfddcecb4" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-7098-7a81-9ef7-e24de204ab78" xlink:type="arc" order="23"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DebtLongtermDebtDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DebtLongtermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DebtLongtermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019dd587-7098-762f-89b8-13e0303ed265" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_DebtInstrumentTable_019dd587-7098-762f-89b8-13e0303ed265" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7865-b6ac-df7a62874481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-7098-762f-89b8-13e0303ed265" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7865-b6ac-df7a62874481" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7865-b6ac-df7a62874481_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7865-b6ac-df7a62874481" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7865-b6ac-df7a62874481_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7865-b6ac-df7a62874481" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-7098-7300-99cf-75aa2107e49c" xlink:href="dpl-20260331.xsd#dpl_A3.95SeniorNotesdue2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A3.95SeniorNotesdue2049Member_019dd587-7098-7300-99cf-75aa2107e49c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-7098-770a-80e7-be72c0ab6471" xlink:href="dpl-20260331.xsd#dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_DPLRevolvingCreditAgreementandTermLoanMaturingJuly2020Member_019dd587-7098-770a-80e7-be72c0ab6471" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-7098-7719-85cf-b9cca34471b6" xlink:href="dpl-20260331.xsd#dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_FourPointTwoZeroPercentageOfUSGovernmentNoteMaturingInFebruaryTwoThousandSixtyOneMember_019dd587-7098-7719-85cf-b9cca34471b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A4.35SeniorNotesdue2029Member_019dd587-7098-740d-b3ec-51a90484f6f7" xlink:href="dpl-20260331.xsd#dpl_A4.35SeniorNotesdue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A4.35SeniorNotesdue2029Member_019dd587-7098-740d-b3ec-51a90484f6f7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember_019dd587-7098-7421-931e-a229807c4e7d" xlink:href="dpl-20260331.xsd#dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_EightPointOneTwoFivePercentageOfNoteToCapitalTrustIIMaturingInSeptemberTwoThousandThirtyOneMember_019dd587-7098-7421-931e-a229807c4e7d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A413SeniorNotesDue2025Member_019dd587-7098-7675-9954-779ad7f09efa" xlink:href="dpl-20260331.xsd#dpl_A413SeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A413SeniorNotesDue2025Member_019dd587-7098-7675-9954-779ad7f09efa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-7098-78c1-aaf6-d56128383a2a" xlink:href="dpl-20260331.xsd#dpl_A320FirstMortgageBondsDue2040Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A320FirstMortgageBondsDue2040Member_019dd587-7098-78c1-aaf6-d56128383a2a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-70c0-ae42-03c17f3678ed" xlink:href="dpl-20260331.xsd#dpl_A425TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A425TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-70c0-ae42-03c17f3678ed" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-7874-9221-0b4e40814db3" xlink:href="dpl-20260331.xsd#dpl_A400TaxExemptFirstMortgageBondsDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A400TaxExemptFirstMortgageBondsDue2027Member_019dd587-7098-7874-9221-0b4e40814db3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-7098-7483-a65d-7f91a7e8b556" xlink:href="dpl-20260331.xsd#dpl_A519FirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A519FirstMortgageBondsDue2033Member_019dd587-7098-7483-a65d-7f91a7e8b556" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70SeniorNotesDue2033Member_019dd587-7098-75b7-b922-548021d949a2" xlink:href="dpl-20260331.xsd#dpl_A5.70SeniorNotesDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A5.70SeniorNotesDue2033Member_019dd587-7098-75b7-b922-548021d949a2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-7098-78da-8e27-c248674cf8c8" xlink:href="dpl-20260331.xsd#dpl_A5.49SeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A5.49SeniorNotesDue2028Member_019dd587-7098-78da-8e27-c248674cf8c8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-7098-79ec-a88e-2afa0b119bdc" xlink:href="dpl-20260331.xsd#dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A5.70TaxExemptFirstMortgageBondsDue2033Member_019dd587-7098-79ec-a88e-2afa0b119bdc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-7098-7326-99e5-7b67e138ee22" xlink:href="dpl-20260331.xsd#dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7473-8627-4a220732ef53" xlink:to="loc_dpl_A5.49TaxExemptFirstMortgageBondsDue2028Member_019dd587-7098-7326-99e5-7b67e138ee22" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-7098-7508-b9fc-18f92ea00d52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019dd587-7098-762f-89b8-13e0303ed265" xlink:to="loc_srt_StatementScenarioAxis_019dd587-7098-7508-b9fc-18f92ea00d52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7508-b9fc-18f92ea00d52_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7508-b9fc-18f92ea00d52" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7508-b9fc-18f92ea00d52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7db7-b430-1856b5e95fdd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7508-b9fc-18f92ea00d52" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7db7-b430-1856b5e95fdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-7098-720e-a9f3-785df9ff2814" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7db7-b430-1856b5e95fdd" xlink:to="loc_srt_ScenarioForecastMember_019dd587-7098-720e-a9f3-785df9ff2814" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-7098-74f8-bd02-e88c2f80cdaf" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_DebtCovenantTotalDebttoTotalCapitalizationRatioMaximum_019dd587-7098-74f8-bd02-e88c2f80cdaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-7098-75d9-876a-ab8e05ae9280" xlink:href="dpl-20260331.xsd#dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_DeferredFinanceCostsNetIncludingAcquisitionAdjustments_019dd587-7098-75d9-876a-ab8e05ae9280" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019dd587-7098-7567-9ac7-8c6f48921fda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019dd587-7098-7567-9ac7-8c6f48921fda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments_019dd587-7098-7549-b608-e7de0853302b" xlink:href="dpl-20260331.xsd#dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_TotalLongtermDebtAtSubsidiaryWithPurchaseAccountingAdjustments_019dd587-7098-7549-b608-e7de0853302b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019dd587-7098-7b9f-b4de-5c86f03255e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_LongTermDebt_019dd587-7098-7b9f-b4de-5c86f03255e3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7098-717f-b759-04160f6c2445" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019dd587-7098-717f-b759-04160f6c2445" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-7098-7a86-851a-5f5dd71eb44c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dd587-7098-7a86-851a-5f5dd71eb44c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-7098-7bd5-8faf-ba3a3be6387b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019dd587-7098-7bd5-8faf-ba3a3be6387b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dd587-7098-7bbe-b990-76a646fd8def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_LineOfCredit_019dd587-7098-7bbe-b990-76a646fd8def" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-7098-7ea7-a5c6-5f6b3ada6903" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantInterestCoverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_DebtCovenantInterestCoverageRatioMinimum_019dd587-7098-7ea7-a5c6-5f6b3ada6903" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-7098-7c68-8168-7d86014e3b93" xlink:href="dpl-20260331.xsd#dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_DebtInstrumentDebtCovenantEBITDAToInterestExpenseEBITDAMinimum_019dd587-7098-7c68-8168-7d86014e3b93" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7098-79a1-87f6-d8e999d1942d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019dd587-7098-79a1-87f6-d8e999d1942d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-7098-74e0-94d5-c4b0e364188f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019dd587-7098-74e0-94d5-c4b0e364188f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-7098-7427-8d3b-d6049ca4bc60" xlink:href="dpl-20260331.xsd#dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019dd587-7098-71f7-8278-9bf6186a8f87" xlink:to="loc_dpl_DebtCovenantTotalDebtToTotalCapitalizationRatioMaximumUpperRange_019dd587-7098-7427-8d3b-d6049ca4bc60" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019dd587-7098-7d88-a40e-121b98fb6dd9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:to="loc_dei_EntitiesTable_019dd587-7098-7d88-a40e-121b98fb6dd9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7756-8bc6-97553bb28635" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019dd587-7098-7d88-a40e-121b98fb6dd9" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7756-8bc6-97553bb28635" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7756-8bc6-97553bb28635_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7756-8bc6-97553bb28635" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7756-8bc6-97553bb28635_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-72ce-8702-9b05f43d398c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7756-8bc6-97553bb28635" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-72ce-8702-9b05f43d398c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7f10-ab29-64256d125046" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-72ce-8702-9b05f43d398c" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7f10-ab29-64256d125046" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019dd587-7098-7b40-8d05-65ab484f38ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019dd587-7098-7b40-8d05-65ab484f38ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-7098-79ef-93b1-d326ab4c7250" xlink:href="dpl-20260331.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-7098-79ef-93b1-d326ab4c7250" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent_019dd587-7098-748e-a2d1-1079fb1b89c0" xlink:href="dpl-20260331.xsd#dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:to="loc_dpl_EffectiveIncomeTaxRateReconciliationIncludingDiscontinuedOperationsPercent_019dd587-7098-748e-a2d1-1079fb1b89c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019dd587-7098-724a-a227-4681f4958307" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019dd587-7098-7669-9200-ea9b4f30897a" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019dd587-7098-724a-a227-4681f4958307" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-7098-7932-b30d-34b132549b79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019dd587-7098-7779-840b-c6fab37395bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-7098-7932-b30d-34b132549b79" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019dd587-7098-7779-840b-c6fab37395bc" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-7098-7571-af9c-18a95d7aa7bc" xlink:href="dpl-20260331.xsd#dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019dd587-7098-7932-b30d-34b132549b79" xlink:to="loc_dpl_EstimatedAnnualEffectiveIncomeTaxRateContinuingOperations_019dd587-7098-7571-af9c-18a95d7aa7bc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansNetPeriodicBenefitCostIncomeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansNetPeriodicBenefitCostIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansNetPeriodicBenefitCostIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-73d0-8663-f11360d5229e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-73d0-8663-f11360d5229e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7806-bfa9-72a0991d7c3b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-73d0-8663-f11360d5229e" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7806-bfa9-72a0991d7c3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7806-bfa9-72a0991d7c3b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7806-bfa9-72a0991d7c3b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7806-bfa9-72a0991d7c3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7e28-835c-46349d2df771" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7806-bfa9-72a0991d7c3b" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7e28-835c-46349d2df771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7aaf-8150-63c5478f4ad1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7e28-835c-46349d2df771" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7aaf-8150-63c5478f4ad1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7154-a306-a96eea03a74b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-73d0-8663-f11360d5229e" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7154-a306-a96eea03a74b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7154-a306-a96eea03a74b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7154-a306-a96eea03a74b" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7154-a306-a96eea03a74b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-73a7-821e-23bade3c089a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-7154-a306-a96eea03a74b" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-73a7-821e-23bade3c089a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-7341-8068-6960c8f6f13f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-73a7-821e-23bade3c089a" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-7341-8068-6960c8f6f13f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-7098-7c41-8824-ad7621139855" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-73a7-821e-23bade3c089a" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-7098-7c41-8824-ad7621139855" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019dd587-7098-72cc-aab4-50f2bb757d88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019dd587-7098-72cc-aab4-50f2bb757d88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_019dd587-7098-7234-a48d-a4cf9056b63f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_019dd587-7098-7234-a48d-a4cf9056b63f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_019dd587-7098-7582-9da7-859cddd7283d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_019dd587-7098-7582-9da7-859cddd7283d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019dd587-7098-75b4-b88d-7457810dc3e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019dd587-7098-75b4-b88d-7457810dc3e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019dd587-7098-7ecb-b791-9715600cbe33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019dd587-7098-7ecb-b791-9715600cbe33" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019dd587-7098-7cc1-858e-4961197fc7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019dd587-7098-7cc1-858e-4961197fc7c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019dd587-7098-71c0-aca4-042846af826a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019dd587-7098-71c0-aca4-042846af826a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-7098-7620-821d-61986178bd0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-750c-87a2-dc70e972dad7" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-7098-7620-821d-61986178bd0b" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BenefitPlansEstimatedFutureBenefitPaymentsandMedicarePartDReimbursementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7098-7dad-afa3-cba39f1bfea2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-7808-b424-318325cb71b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7dad-afa3-cba39f1bfea2" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-7808-b424-318325cb71b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7d75-b324-25f1b4acd6e1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-7808-b424-318325cb71b4" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7d75-b324-25f1b4acd6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7d75-b324-25f1b4acd6e1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7d75-b324-25f1b4acd6e1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7d75-b324-25f1b4acd6e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c57-8969-c2f2252b6c8c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7d75-b324-25f1b4acd6e1" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c57-8969-c2f2252b6c8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-733a-9e04-005abc669caf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c57-8969-c2f2252b6c8c" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-733a-9e04-005abc669caf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-724a-9870-ce4f7d6ade0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019dd587-7098-7808-b424-318325cb71b4" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-724a-9870-ce4f7d6ade0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-724a-9870-ce4f7d6ade0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-724a-9870-ce4f7d6ade0a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-724a-9870-ce4f7d6ade0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7a30-9d4a-d3f1722a9fbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019dd587-7098-724a-9870-ce4f7d6ade0a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7a30-9d4a-d3f1722a9fbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-788f-914a-f876c4c71669" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7a30-9d4a-d3f1722a9fbf" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019dd587-7098-788f-914a-f876c4c71669" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-7098-7c46-b060-066ed3fe489c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019dd587-7098-7a30-9d4a-d3f1722a9fbf" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019dd587-7098-7c46-b060-066ed3fe489c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-7098-750e-801b-41724f468722" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7dad-afa3-cba39f1bfea2" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_019dd587-7098-750e-801b-41724f468722" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/EquityDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#EquityDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/EquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7da2-b679-f3519683074c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7da2-b679-f3519683074c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7da2-b679-f3519683074c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7da2-b679-f3519683074c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7da2-b679-f3519683074c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7c46-86f1-234b171498ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019dd587-7098-7da2-b679-f3519683074c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7c46-86f1-234b171498ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019dd587-7098-7a8f-b4c9-de5c35e6b46e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019dd587-7098-7c46-86f1-234b171498ff" xlink:to="loc_us-gaap_SubsequentEventMember_019dd587-7098-7a8f-b4c9-de5c35e6b46e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7cf1-a67d-a88a4a340a52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7cf1-a67d-a88a4a340a52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7cf1-a67d-a88a4a340a52_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7cf1-a67d-a88a4a340a52" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7cf1-a67d-a88a4a340a52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c85-9102-4aaf088570f6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7cf1-a67d-a88a4a340a52" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c85-9102-4aaf088570f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7a05-abf3-ea53c1483d2b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7c85-9102-4aaf088570f6" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7a05-abf3-ea53c1483d2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-7098-7ce4-a546-e113a3924441" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:to="loc_srt_StatementScenarioAxis_019dd587-7098-7ce4-a546-e113a3924441" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7ce4-a546-e113a3924441_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7ce4-a546-e113a3924441" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-7ce4-a546-e113a3924441_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-766a-888a-74982c3cae73" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-7098-7ce4-a546-e113a3924441" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-766a-888a-74982c3cae73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-7098-7cc2-9e5a-e0283b21f0d8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-7098-766a-888a-74982c3cae73" xlink:to="loc_srt_ScenarioForecastMember_019dd587-7098-7cc2-9e5a-e0283b21f0d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7098-7c0e-9c5e-b08eee028fc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-7098-7c5e-bf68-57a9cd6e13ad" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7098-7c0e-9c5e-b08eee028fc8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7098-7c0e-9c5e-b08eee028fc8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7098-7c0e-9c5e-b08eee028fc8" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7098-7c0e-9c5e-b08eee028fc8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dd587-7098-7423-b99d-f354db3c4622" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dd587-7098-7c0e-9c5e-b08eee028fc8" xlink:to="loc_us-gaap_EquityComponentDomain_019dd587-7098-7423-b99d-f354db3c4622" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-7098-7247-80db-7433ab4690c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAdditionalCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7098-7423-b99d-f354db3c4622" xlink:to="loc_us-gaap_OtherAdditionalCapitalMember_019dd587-7098-7247-80db-7433ab4690c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7098-798c-a964-f223069d11d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dd587-7098-7423-b99d-f354db3c4622" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019dd587-7098-798c-a964-f223069d11d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_019dd587-7098-7315-807d-8b13792a7ca4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_019dd587-7098-7315-807d-8b13792a7ca4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CashContributionFromParentCompany_019dd587-7098-7902-ab96-3b838ecb9819" xlink:href="dpl-20260331.xsd#dpl_CashContributionFromParentCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_dpl_CashContributionFromParentCompany_019dd587-7098-7902-ab96-3b838ecb9819" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-7098-7a8f-910f-0b561f29c517" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_019dd587-7098-7a8f-910f-0b561f29c517" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Noncashcapitalcontribution_019dd587-7098-70b7-b5a8-76f086b2d030" xlink:href="dpl-20260331.xsd#dpl_Noncashcapitalcontribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_dpl_Noncashcapitalcontribution_019dd587-7098-70b7-b5a8-76f086b2d030" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PaymentAgainstTaxReceivableBalanceFromParent_019dd587-7098-72fc-beec-cf0f308c01fc" xlink:href="dpl-20260331.xsd#dpl_PaymentAgainstTaxReceivableBalanceFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_dpl_PaymentAgainstTaxReceivableBalanceFromParent_019dd587-7098-72fc-beec-cf0f308c01fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019dd587-7098-79d9-9776-849906fc584f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_StockholdersEquityOther_019dd587-7098-79d9-9776-849906fc584f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7098-7a94-9950-3d5460eb7243" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019dd587-7098-7a94-9950-3d5460eb7243" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7098-7e3c-a4e3-150e630fd0aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_019dd587-7098-7e3c-a4e3-150e630fd0aa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-7098-7504-bfd4-1335ca862089" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019dd587-7098-7504-bfd4-1335ca862089" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityContributionFromParent_019dda05-029c-7f67-b5b2-b259d400c5d3" xlink:href="dpl-20260331.xsd#dpl_EquityContributionFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-7098-7528-8f38-5cd481e7069f" xlink:to="loc_dpl_EquityContributionFromParent_019dda05-029c-7f67-b5b2-b259d400c5d3" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/ContractualObligationsCommercialCommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-7098-789b-89d5-8d1da42cbc10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-7098-76cd-a4e5-f24dc131fd06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PublicUtilityPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-7098-789b-89d5-8d1da42cbc10" xlink:to="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-7098-76cd-a4e5-f24dc131fd06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-7098-797e-a526-83fb70668f05" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-7098-76cd-a4e5-f24dc131fd06" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-7098-797e-a526-83fb70668f05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019dd587-7098-797e-a526-83fb70668f05_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-7098-797e-a526-83fb70668f05" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019dd587-7098-797e-a526-83fb70668f05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019dd587-7098-7847-ab06-fe361912a8f0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019dd587-7098-797e-a526-83fb70668f05" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019dd587-7098-7847-ab06-fe361912a8f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricGenerationCompanyMember_019dd587-7098-747b-bb9b-400468fb8268" xlink:href="dpl-20260331.xsd#dpl_ElectricGenerationCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019dd587-7098-7847-ab06-fe361912a8f0" xlink:to="loc_dpl_ElectricGenerationCompanyMember_019dd587-7098-747b-bb9b-400468fb8268" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7d21-b4aa-b16022142d82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-7098-76cd-a4e5-f24dc131fd06" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7d21-b4aa-b16022142d82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7d21-b4aa-b16022142d82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7d21-b4aa-b16022142d82" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-7d21-b4aa-b16022142d82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-724e-9d44-7c4638bd0b29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dd587-7098-7d21-b4aa-b16022142d82" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-724e-9d44-7c4638bd0b29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DebtObligationOn49EquityOwnershipMember_019dd587-7098-7cb5-acdf-9906ef3fbbc4" xlink:href="dpl-20260331.xsd#dpl_DebtObligationOn49EquityOwnershipMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dd587-7098-724e-9d44-7c4638bd0b29" xlink:to="loc_dpl_DebtObligationOn49EquityOwnershipMember_019dd587-7098-7cb5-acdf-9906ef3fbbc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7650-b34e-424cf1ee1f54" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentTable_019dd587-7098-76cd-a4e5-f24dc131fd06" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7650-b34e-424cf1ee1f54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7650-b34e-424cf1ee1f54_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7650-b34e-424cf1ee1f54" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-7650-b34e-424cf1ee1f54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-726c-9031-49633389ccc7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-7098-7650-b34e-424cf1ee1f54" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-726c-9031-49633389ccc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-7098-7103-ad05-50335e139856" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-7098-726c-9031-49633389ccc7" xlink:to="loc_srt_SubsidiariesMember_019dd587-7098-7103-ad05-50335e139856" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_019dd587-7098-76de-9dd8-1bca36447c90" xlink:href="dpl-20260331.xsd#dpl_PublicUtilitiesEquityInterestCostMethodPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-7098-789b-89d5-8d1da42cbc10" xlink:to="loc_dpl_PublicUtilitiesEquityInterestCostMethodPercentage_019dd587-7098-76de-9dd8-1bca36447c90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_019dd587-7098-7450-8025-d385dbb7c638" xlink:href="dpl-20260331.xsd#dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-7098-789b-89d5-8d1da42cbc10" xlink:to="loc_dpl_EquityOwnershipInterestGuaranteedPortionofLongtermDebtObligation_019dd587-7098-7450-8025-d385dbb7c638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019dd587-7098-7abe-9ec6-d0b9305331e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems_019dd587-7098-789b-89d5-8d1da42cbc10" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019dd587-7098-7abe-9ec6-d0b9305331e2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsNarrativeDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-714d-79dd-8570-4ff30e6dad0f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-714d-79dd-8570-4ff30e6dad0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-79dd-8570-4ff30e6dad0f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-79dd-8570-4ff30e6dad0f" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-79dd-8570-4ff30e6dad0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-7094-9200-1291ac4bd93e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-79dd-8570-4ff30e6dad0f" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-7094-9200-1291ac4bd93e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-714d-7209-97df-23b82ffaee0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7094-9200-1291ac4bd93e" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-714d-7209-97df-23b82ffaee0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019dd587-714d-7171-be94-5b6ecc83677c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7094-9200-1291ac4bd93e" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019dd587-714d-7171-be94-5b6ecc83677c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_019dd587-714d-7b4c-8d9f-978ed17eb656" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7094-9200-1291ac4bd93e" xlink:to="loc_us-gaap_IntersegmentEliminationMember_019dd587-714d-7b4c-8d9f-978ed17eb656" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-7a30-a01c-dab528597bf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-7a30-a01c-dab528597bf3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-7a30-a01c-dab528597bf3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-7a30-a01c-dab528597bf3" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-7a30-a01c-dab528597bf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-7cd5-90a5-7e4499d243b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-7a30-a01c-dab528597bf3" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-7cd5-90a5-7e4499d243b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-714d-73d7-a891-9cc20786c838" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-7cd5-90a5-7e4499d243b2" xlink:to="loc_dpl_UtilityMember_019dd587-714d-73d7-a891-9cc20786c838" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019dd587-714d-71c5-b730-1b0ca56dbc15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-7cd5-90a5-7e4499d243b2" xlink:to="loc_us-gaap_CorporateAndOtherMember_019dd587-714d-71c5-b730-1b0ca56dbc15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-723b-8b33-11e2c671d189" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-723b-8b33-11e2c671d189" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-723b-8b33-11e2c671d189_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-723b-8b33-11e2c671d189" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-723b-8b33-11e2c671d189_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e33-bde6-a8bca680127c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-723b-8b33-11e2c671d189" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e33-bde6-a8bca680127c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7fa6-81de-24c2c9d17a10" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e33-bde6-a8bca680127c" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7fa6-81de-24c2c9d17a10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-793a-ab20-b02391aa3284" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-793a-ab20-b02391aa3284" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-793a-ab20-b02391aa3284_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-793a-ab20-b02391aa3284" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-793a-ab20-b02391aa3284_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7725-82b8-53fdfe14467e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-793a-ab20-b02391aa3284" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7725-82b8-53fdfe14467e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-714d-7d96-997a-23bbd351a03d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7725-82b8-53fdfe14467e" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-714d-7d96-997a-23bbd351a03d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-714d-7d07-8852-91109777bcc2" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-7723-8ea5-5239515157eb" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-714d-7d07-8852-91109777bcc2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-7d07-8852-91109777bcc2_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-7d07-8852-91109777bcc2" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-7d07-8852-91109777bcc2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-77c4-9e63-97c803c3f06f" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-7d07-8852-91109777bcc2" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-77c4-9e63-97c803c3f06f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueFromExternalCustomersMember_019dd587-714d-7e79-98d0-61173d5be26b" xlink:href="dpl-20260331.xsd#dpl_RevenueFromExternalCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-77c4-9e63-97c803c3f06f" xlink:to="loc_dpl_RevenueFromExternalCustomersMember_019dd587-714d-7e79-98d0-61173d5be26b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IntersegmentRevenueMember_019dd587-714d-7699-8823-e089899d574e" xlink:href="dpl-20260331.xsd#dpl_IntersegmentRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-77c4-9e63-97c803c3f06f" xlink:to="loc_dpl_IntersegmentRevenueMember_019dd587-714d-7699-8823-e089899d574e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019dd587-714d-7eed-ac8f-5067126bd5ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019dd587-714d-7eed-ac8f-5067126bd5ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_NumberOfRetailCustomers_019dd587-714d-7019-9cd0-a87993648c15" xlink:href="dpl-20260331.xsd#dpl_NumberOfRetailCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_dpl_NumberOfRetailCustomers_019dd587-714d-7019-9cd0-a87993648c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ServiceAreaSquareMiles_019dd587-714d-7fee-8f62-36d34abee55d" xlink:href="dpl-20260331.xsd#dpl_ServiceAreaSquareMiles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_dpl_ServiceAreaSquareMiles_019dd587-714d-7fee-8f62-36d34abee55d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-714d-7a89-94f5-615e0e172a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_Assets_019dd587-714d-7a89-94f5-615e0e172a9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-714d-72a0-8129-17f68b3133b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_Revenues_019dd587-714d-72a0-8129-17f68b3133b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-714d-7cbe-bb28-dfaadb6c6eb4" xlink:href="dpl-20260331.xsd#dpl_ElectricRevenueIncludingDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-714d-7cbe-bb28-dfaadb6c6eb4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-714d-7189-b984-c37b1869fb20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpensePurchasedPower"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-714d-7189-b984-c37b1869fb20" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-714d-7b8e-bff0-6beee8d5c8f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-714d-7b8e-bff0-6beee8d5c8f3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-714d-7638-ba9b-6e8cdcdc1f90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-714d-7638-ba9b-6e8cdcdc1f90" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-714d-7477-810a-6fd668b7a06a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-714d-7477-810a-6fd668b7a06a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-714d-71cc-9540-83474bec7bd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-714d-71cc-9540-83474bec7bd0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-714d-70b8-ac5a-80c01b06b0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-714d-70b8-ac5a-80c01b06b0cc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dda0e-aa21-7f1e-9936-21d04f2e42e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dda0e-aa21-7f1e-9936-21d04f2e42e9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-714d-77d8-9282-2e3be3f8ebfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-714d-77d8-9282-2e3be3f8ebfe" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-714d-70d5-9a0f-caae32705d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-714d-70d5-9a0f-caae32705d0e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-714d-7ce5-9493-7b92b203e0d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-714d-7ce5-9493-7b92b203e0d5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-714d-7b61-ada2-93e0859cf53a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-7658-997a-6bed399bfec2" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-714d-7b61-ada2-93e0859cf53a" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/BusinessSegmentsSegmentFinancialInformationDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#BusinessSegmentsSegmentFinancialInformationDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/BusinessSegmentsSegmentFinancialInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7d33-85f9-16d2918f35f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7d33-85f9-16d2918f35f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7d33-85f9-16d2918f35f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7d33-85f9-16d2918f35f1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7d33-85f9-16d2918f35f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7794-8abf-04a02f0a95f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7d33-85f9-16d2918f35f1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7794-8abf-04a02f0a95f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e82-8104-d0c0db2e7019" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e82-8104-d0c0db2e7019" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e82-8104-d0c0db2e7019_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e82-8104-d0c0db2e7019" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7e82-8104-d0c0db2e7019_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f45-befc-c3dad621353f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7e82-8104-d0c0db2e7019" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f45-befc-c3dad621353f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7e96-8e96-0f37491dd006" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7f45-befc-c3dad621353f" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7e96-8e96-0f37491dd006" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019dd587-714d-7d8b-ba0b-2d063abbe3ac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_srt_ConsolidationItemsAxis_019dd587-714d-7d8b-ba0b-2d063abbe3ac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-7d8b-ba0b-2d063abbe3ac_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-7d8b-ba0b-2d063abbe3ac" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-7d8b-ba0b-2d063abbe3ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019dd587-714d-7d8b-ba0b-2d063abbe3ac" xlink:to="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019dd587-714d-719e-97ad-f8e6117633b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:to="loc_us-gaap_OperatingSegmentsMember_019dd587-714d-719e-97ad-f8e6117633b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019dd587-714d-7088-8836-14cb2f229600" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019dd587-714d-7088-8836-14cb2f229600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_019dd587-714d-73f4-974c-ec8a11d4e1ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:to="loc_us-gaap_IntersegmentEliminationMember_019dd587-714d-73f4-974c-ec8a11d4e1ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_019dd587-714d-772b-8d52-5c32e3b75d98" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019dd587-714d-7014-a0b5-bb01e5e67d92" xlink:to="loc_srt_ConsolidationEliminationsMember_019dd587-714d-772b-8d52-5c32e3b75d98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-744d-a536-4c8207aef9af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-744d-a536-4c8207aef9af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-744d-a536-4c8207aef9af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-744d-a536-4c8207aef9af" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-744d-a536-4c8207aef9af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-737e-96cd-a29aea2dacb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-744d-a536-4c8207aef9af" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-737e-96cd-a29aea2dacb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-714d-75d4-90d6-4af1d37a8b08" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-737e-96cd-a29aea2dacb1" xlink:to="loc_dpl_UtilityMember_019dd587-714d-75d4-90d6-4af1d37a8b08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-7275-a532-0be9347c8d17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-7275-a532-0be9347c8d17" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7275-a532-0be9347c8d17_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-7275-a532-0be9347c8d17" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7275-a532-0be9347c8d17_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7fe9-a5f9-c1b7c291274e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019dd587-714d-7275-a532-0be9347c8d17" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7fe9-a5f9-c1b7c291274e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019dd587-714d-74c9-9d3e-ba97327480cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019dd587-714d-7fe9-a5f9-c1b7c291274e" xlink:to="loc_us-gaap_RelatedPartyMember_019dd587-714d-74c9-9d3e-ba97327480cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-714d-7407-a6dd-3b92ad84db63" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019dd587-714d-715e-9c8c-9cf3cb409b87" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-714d-7407-a6dd-3b92ad84db63" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-7407-a6dd-3b92ad84db63_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-7407-a6dd-3b92ad84db63" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-7407-a6dd-3b92ad84db63_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-71eb-be37-b089d2aeb3bf" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-7407-a6dd-3b92ad84db63" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-71eb-be37-b089d2aeb3bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueFromExternalCustomersMember_019dd587-714d-7095-aba3-c25c7c104197" xlink:href="dpl-20260331.xsd#dpl_RevenueFromExternalCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-71eb-be37-b089d2aeb3bf" xlink:to="loc_dpl_RevenueFromExternalCustomersMember_019dd587-714d-7095-aba3-c25c7c104197" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IntersegmentRevenueMember_019dd587-714d-7293-9053-03f5b7b3e15d" xlink:href="dpl-20260331.xsd#dpl_IntersegmentRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-71eb-be37-b089d2aeb3bf" xlink:to="loc_dpl_IntersegmentRevenueMember_019dd587-714d-7293-9053-03f5b7b3e15d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ExternalCustomerRevenues_019dd587-714d-74a6-a643-9605c5cabf9f" xlink:href="dpl-20260331.xsd#dpl_ExternalCustomerRevenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_dpl_ExternalCustomerRevenues_019dd587-714d-74a6-a643-9605c5cabf9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-714d-7a22-808e-016154fdea1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_Revenues_019dd587-714d-7a22-808e-016154fdea1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-714d-7d91-863b-a2a795adccc5" xlink:href="dpl-20260331.xsd#dpl_ElectricRevenueIncludingDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_dpl_ElectricRevenueIncludingDiscontinuedOperations_019dd587-714d-7d91-863b-a2a795adccc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-714d-7e4e-ab03-fcff499c1ddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019dd587-714d-7e4e-ab03-fcff499c1ddc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_019dd587-714d-792a-990f-ddce79a454f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_InterestAndDebtExpense_019dd587-714d-792a-990f-ddce79a454f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dd587-714d-7811-8add-109979db1315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dd587-714d-7811-8add-109979db1315" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019dd587-714d-79a0-8065-8073f5fe042a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_Assets_019dd587-714d-79a0-8065-8073f5fe042a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-714d-720a-bac8-1fd8018eec21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019dd587-714d-720a-bac8-1fd8018eec21" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-714d-76ca-84db-afac55f543d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpensePurchasedPower"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_UtilitiesOperatingExpensePurchasedPower_019dd587-714d-76ca-84db-afac55f543d4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-714d-76b6-a74b-2bc5ff8b4003" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_019dd587-714d-76b6-a74b-2bc5ff8b4003" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-714d-71ba-a6e2-fa0c5aaf1ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_019dd587-714d-71ba-a6e2-fa0c5aaf1ae8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_019dd587-714d-764f-b92e-508bc252c090" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_OtherExpenses_019dd587-714d-764f-b92e-508bc252c090" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-714d-72ad-834d-766d05a9bf2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019dd587-714d-72ad-834d-766d05a9bf2c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-714d-7ab9-a0ca-ba565e0b21d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019dd587-714d-7ab9-a0ca-ba565e0b21d9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-714d-759d-8578-c24ef36c17d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019dd587-714d-759d-8578-c24ef36c17d5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019dd587-714d-7069-a73d-d94ed49f9ed9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_NetIncomeLoss_019dd587-714d-7069-a73d-d94ed49f9ed9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-714d-78f4-859d-ccb86161ce67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019dd587-714d-78f4-859d-ccb86161ce67" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-714d-7961-a2ac-a8721ac12d68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019dd587-714d-78d4-b1ff-5d61a0b17567" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019dd587-714d-7961-a2ac-a8721ac12d68" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RevenueDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RevenueDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019dd587-714d-73d7-8a18-9b38767b8e33" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:to="loc_srt_ProductOrServiceAxis_019dd587-714d-73d7-8a18-9b38767b8e33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dd587-714d-73d7-8a18-9b38767b8e33_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019dd587-714d-73d7-8a18-9b38767b8e33" xlink:to="loc_srt_ProductsAndServicesDomain_019dd587-714d-73d7-8a18-9b38767b8e33_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dd587-714d-7339-8d7d-3b99e1b83311" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019dd587-714d-73d7-8a18-9b38767b8e33" xlink:to="loc_srt_ProductsAndServicesDomain_019dd587-714d-7339-8d7d-3b99e1b83311" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_019dd587-714d-7886-ac99-e11ab5bf67c1" xlink:href="dpl-20260331.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-714d-7339-8d7d-3b99e1b83311" xlink:to="loc_dpl_OtherRevenuesMember_019dd587-714d-7886-ac99-e11ab5bf67c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_WholesaleRevenueMember_019dd587-714d-7979-b660-0542fda20acc" xlink:href="dpl-20260331.xsd#dpl_WholesaleRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-714d-7339-8d7d-3b99e1b83311" xlink:to="loc_dpl_WholesaleRevenueMember_019dd587-714d-7979-b660-0542fda20acc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RetailRevenueMember_019dd587-714d-7183-825a-317a56e517b1" xlink:href="dpl-20260331.xsd#dpl_RetailRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dd587-714d-7339-8d7d-3b99e1b83311" xlink:to="loc_dpl_RetailRevenueMember_019dd587-714d-7183-825a-317a56e517b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-772e-a446-3ff9af6b82e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-772e-a446-3ff9af6b82e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-772e-a446-3ff9af6b82e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-772e-a446-3ff9af6b82e5" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-772e-a446-3ff9af6b82e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019dd587-714d-7bc3-9421-be7482d37413" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019dd587-714d-772e-a446-3ff9af6b82e5" xlink:to="loc_us-gaap_SegmentDomain_019dd587-714d-7bc3-9421-be7482d37413" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_UtilityMember_019dd587-714d-7f2d-aded-bc7d0c874bed" xlink:href="dpl-20260331.xsd#dpl_UtilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-7bc3-9421-be7482d37413" xlink:to="loc_dpl_UtilityMember_019dd587-714d-7f2d-aded-bc7d0c874bed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019dd587-714d-75ff-9543-3791b7b451c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-7bc3-9421-be7482d37413" xlink:to="loc_us-gaap_CorporateAndOtherMember_019dd587-714d-75ff-9543-3791b7b451c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_AdjustmentsAndEliminationsMember_019dd587-714d-7671-952e-fa03ef687055" xlink:href="dpl-20260331.xsd#dpl_AdjustmentsAndEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019dd587-714d-7bc3-9421-be7482d37413" xlink:to="loc_dpl_AdjustmentsAndEliminationsMember_019dd587-714d-7671-952e-fa03ef687055" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeAxis_019dd587-714d-722b-9e86-0856b60b1d93" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:to="loc_dpl_RevenueTypeAxis_019dd587-714d-722b-9e86-0856b60b1d93" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-722b-9e86-0856b60b1d93_default" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-722b-9e86-0856b60b1d93" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-722b-9e86-0856b60b1d93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:href="dpl-20260331.xsd#dpl_RevenueTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dpl_RevenueTypeAxis_019dd587-714d-722b-9e86-0856b60b1d93" xlink:to="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ResidentialRevenueMember_019dd587-714d-7100-80e1-d9bd05f7a38e" xlink:href="dpl-20260331.xsd#dpl_ResidentialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:to="loc_dpl_ResidentialRevenueMember_019dd587-714d-7100-80e1-d9bd05f7a38e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_CommercialRevenueMember_019dd587-714d-7d97-9d01-5ab9571cd588" xlink:href="dpl-20260331.xsd#dpl_CommercialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:to="loc_dpl_CommercialRevenueMember_019dd587-714d-7d97-9d01-5ab9571cd588" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_IndustrialRevenueMember_019dd587-714d-79ed-9e97-270c956ea267" xlink:href="dpl-20260331.xsd#dpl_IndustrialRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:to="loc_dpl_IndustrialRevenueMember_019dd587-714d-79ed-9e97-270c956ea267" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_GovernmentalRevenueMember_019dd587-714d-7275-aa3a-cc0fb5ae7808" xlink:href="dpl-20260331.xsd#dpl_GovernmentalRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:to="loc_dpl_GovernmentalRevenueMember_019dd587-714d-7275-aa3a-cc0fb5ae7808" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_OtherRevenuesMember_019dd587-714d-70a3-a09d-17d0ee1ab68f" xlink:href="dpl-20260331.xsd#dpl_OtherRevenuesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dpl_RevenueTypeDomain_019dd587-714d-7d4d-9f72-94c9cf7cd56c" xlink:to="loc_dpl_OtherRevenuesMember_019dd587-714d-70a3-a09d-17d0ee1ab68f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7fec-bc5c-6d698f4c4e22" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7e89-88dc-acb59dc28050" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7fec-bc5c-6d698f4c4e22" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7fec-bc5c-6d698f4c4e22_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7fec-bc5c-6d698f4c4e22" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7fec-bc5c-6d698f4c4e22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75a5-9e14-c24103daf8c1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7fec-bc5c-6d698f4c4e22" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75a5-9e14-c24103daf8c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7421-8ef0-aae2200075c5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75a5-9e14-c24103daf8c1" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7421-8ef0-aae2200075c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019dd587-714d-7a7d-a1c4-7ebff6f91ac5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019dd587-714d-7a7d-a1c4-7ebff6f91ac5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_Othernon606revenue_019dd587-714d-7c0d-93d8-33c06e8cbbd3" xlink:href="dpl-20260331.xsd#dpl_Othernon606revenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_dpl_Othernon606revenue_019dd587-714d-7c0d-93d8-33c06e8cbbd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTORevenue_019dd587-714d-78c7-8609-14adc6941e39" xlink:href="dpl-20260331.xsd#dpl_RTORevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_dpl_RTORevenue_019dd587-714d-78c7-8609-14adc6941e39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_RTOCapacityRevenue_019dd587-714d-77e9-82e3-5fbb6d109798" xlink:href="dpl-20260331.xsd#dpl_RTOCapacityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_dpl_RTOCapacityRevenue_019dd587-714d-77e9-82e3-5fbb6d109798" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019dd587-714d-7d91-9a7a-781268e26378" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_us-gaap_Revenues_019dd587-714d-7d91-9a7a-781268e26378" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-714d-72fb-bec1-b453cbe20822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-78b1-8af7-7ce4b6b8a40e" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_019dd587-714d-72fb-bec1-b453cbe20822" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/FixedassetImpairmentFixedassetImpairmentDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#FixedassetImpairmentFixedassetImpairmentDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/FixedassetImpairmentFixedassetImpairmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019dd587-714d-7496-969e-eede0e459375" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019dd587-714d-7957-b389-b2e10721b306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019dd587-714d-7496-969e-eede0e459375" xlink:to="loc_us-gaap_StatementTable_019dd587-714d-7957-b389-b2e10721b306" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-714d-7851-83b9-77516717f0be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7957-b389-b2e10721b306" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-714d-7851-83b9-77516717f0be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-714d-7851-83b9-77516717f0be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-714d-7851-83b9-77516717f0be" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-714d-7851-83b9-77516717f0be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-714d-7dce-ac06-0a87cfa5c9ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019dd587-714d-7851-83b9-77516717f0be" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-714d-7dce-ac06-0a87cfa5c9ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019dd587-714d-7f74-a0a3-436df4a3f552" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019dd587-714d-7dce-ac06-0a87cfa5c9ac" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019dd587-714d-7f74-a0a3-436df4a3f552" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-74f0-b6e7-28173cf04265" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019dd587-714d-7957-b389-b2e10721b306" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-74f0-b6e7-28173cf04265" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-74f0-b6e7-28173cf04265_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-74f0-b6e7-28173cf04265" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-74f0-b6e7-28173cf04265_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-71d2-bab2-1858dada79a8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-74f0-b6e7-28173cf04265" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-71d2-bab2-1858dada79a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7c92-ab58-8a849f472448" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-71d2-bab2-1858dada79a8" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7c92-ab58-8a849f472448" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-71e3-bcad-9d48aa051812_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-71e3-bcad-9d48aa051812_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ConesvilleMember_019dd587-714d-7dc7-8776-55895435d4d9" xlink:href="dpl-20260331.xsd#dpl_ConesvilleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:to="loc_dpl_ConesvilleMember_019dd587-714d-7dc7-8776-55895435d4d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-774a-8e5f-9abfea8ec97c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-774a-8e5f-9abfea8ec97c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7551-a8fb-ca4bc00c6a56" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7551-a8fb-ca4bc00c6a56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7bf0-9b91-68816a7c86c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7bf0-9b91-68816a7c86c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7104-8ccc-ee887173f6eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7104-8ccc-ee887173f6eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7387-bb34-862696ac88cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7387-bb34-862696ac88cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7868-9cf3-b84220ff156e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7868-9cf3-b84220ff156e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-7ccd-956e-401589d987f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019dd587-714d-7ccd-956e-401589d987f2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-74eb-8c11-7f962347e0b9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-74eb-8c11-7f962347e0b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-714d-76f2-80b3-9fcd940892b9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:to="loc_srt_ScenarioForecastMember_019dd587-714d-76f2-80b3-9fcd940892b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-714d-7dc5-9ea5-2932a174c630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-714d-7dc5-9ea5-2932a174c630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-714d-72f2-bd40-6b2b2a2503f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-714d-72f2-bd40-6b2b2a2503f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-714d-7c99-9cd0-53eb96744f72" xlink:href="dpl-20260331.xsd#dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-714d-7c99-9cd0-53eb96744f72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-714d-7691-b73c-cddc38782679" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-714d-7691-b73c-cddc38782679" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-714d-7e58-9819-a13b3ca8ee54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-714d-7e58-9819-a13b3ca8ee54" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7d91-9986-f08b61f43e04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7d91-9986-f08b61f43e04" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7533-af04-2f4f008d56b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-7779-bc30-a7533973d667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-7779-bc30-a7533973d667" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-796a-9762-169616584918" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/DiscontinuedOperationsDetails_1" xlink:type="simple" xlink:href="dpl-20260331.xsd#DiscontinuedOperationsDetails_1"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/DiscontinuedOperationsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-71e3-bcad-9d48aa051812_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-71e3-bcad-9d48aa051812_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019dd587-714d-71e3-bcad-9d48aa051812" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_ConesvilleMember_019dd587-714d-7dc7-8776-55895435d4d9" xlink:href="dpl-20260331.xsd#dpl_ConesvilleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019dd587-714d-7c99-8a0a-a7aeefc6dfc6" xlink:to="loc_dpl_ConesvilleMember_019dd587-714d-7dc7-8776-55895435d4d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-774a-8e5f-9abfea8ec97c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-774a-8e5f-9abfea8ec97c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-774a-8e5f-9abfea8ec97c" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7551-a8fb-ca4bc00c6a56" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-742d-8ebc-2fcf17ba86f2" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7551-a8fb-ca4bc00c6a56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7bf0-9b91-68816a7c86c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7bf0-9b91-68816a7c86c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7104-8ccc-ee887173f6eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019dd587-714d-7bf0-9b91-68816a7c86c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019dd587-714d-7104-8ccc-ee887173f6eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7387-bb34-862696ac88cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7387-bb34-862696ac88cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7868-9cf3-b84220ff156e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019dd587-714d-7387-bb34-862696ac88cd" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019dd587-714d-7868-9cf3-b84220ff156e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019dd587-714d-7b0d-8075-f136f12663e6" xlink:to="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-74eb-8c11-7f962347e0b9_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-74eb-8c11-7f962347e0b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dd587-714d-74eb-8c11-7f962347e0b9" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dd587-714d-76f2-80b3-9fcd940892b9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dd587-714d-7b06-8d3b-7c96dc393604" xlink:to="loc_srt_ScenarioForecastMember_019dd587-714d-76f2-80b3-9fcd940892b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-714d-7dc5-9ea5-2932a174c630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromRemovalCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_PaymentsForProceedsFromRemovalCosts_019dd587-714d-7dc5-9ea5-2932a174c630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-714d-72f2-bd40-6b2b2a2503f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019dd587-714d-72f2-bd40-6b2b2a2503f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-714d-7c99-9cd0-53eb96744f72" xlink:href="dpl-20260331.xsd#dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_dpl_DisposalGroupIncludingDiscontinuedOperationOperatingandOtherExpenses_019dd587-714d-7c99-9cd0-53eb96744f72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-714d-7691-b73c-cddc38782679" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019dd587-714d-7691-b73c-cddc38782679" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-714d-7e58-9819-a13b3ca8ee54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019dd587-714d-7e58-9819-a13b3ca8ee54" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7d91-9986-f08b61f43e04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7d91-9986-f08b61f43e04" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_019dd587-714d-7533-af04-2f4f008d56b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-7779-bc30-a7533973d667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019dd587-714d-79a4-b13f-66755be1727a" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-7779-bc30-a7533973d667" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_019dd587-714d-796a-9762-169616584918" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.dpandl.com/role/RiskUncertaintiesDetails" xlink:type="simple" xlink:href="dpl-20260331.xsd#RiskUncertaintiesDetails"/>
  <link:definitionLink xlink:role="http://www.dpandl.com/role/RiskUncertaintiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-714d-7c3e-a275-bbf483226796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-7a72-afdb-3e8e18619b98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_019dd587-714d-7c3e-a275-bbf483226796" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-7a72-afdb-3e8e18619b98" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7637-96d1-4620a2781db0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_019dd587-714d-7a72-afdb-3e8e18619b98" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7637-96d1-4620a2781db0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7637-96d1-4620a2781db0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7637-96d1-4620a2781db0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-7637-96d1-4620a2781db0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75b0-809c-c927e87df2bd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019dd587-714d-7637-96d1-4620a2781db0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75b0-809c-c927e87df2bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_019dd587-714d-7825-8c38-8a845fcb1721" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019dd587-714d-75b0-809c-c927e87df2bd" xlink:to="loc_srt_SubsidiariesMember_019dd587-714d-7825-8c38-8a845fcb1721" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
