The Business Process Definition Metamodel (BPDM) is a standard definition of concepts used to express business process models (a metamodel), adopted by the OMG (Object Management Group).
Pursuant to the OMG's policies, the metamodel is the result of an open process involving submissions by member organizations, following a Request for Proposal (RFP) issued in 2003.
The BPDM specification addresses the objectives of the OMG RFP on which it is based: The RFP seeks to "improve communication between modelers, including between business and software modelers, provide flexible selection of tools and execution environments, and promote the development of more specialised tools for the analysis and design of processes."
They are different in that BPDM provides a specification of semantics integrated in a metamodel, and it includes additional modeling capabilities such as choreography, discussed above.
BPDM implementations are in preparation, including support for BPMN, and translation to XPDL.