A Collaboration represents the interactions between two or more business entities. A Collaboration diagram depicts a global point of view. It shows the interactions between participants in general.
A Collaboration contains two or more pools, representing the participants in the collaboration. Messages exchanged between the participants are shown by message flows that connect two pools together (or objects within the pools).
Collaboration diagram with two Black Box Pools
Collaboration diagram with two Pools showing process
A Collaboration diagram can also show distinct conversations between collaborating participants in a domain. Communications are defined by the conversations, participants, and conversation links between them.
BPMN Collaboration diagram with Conversations
The elements of a BPMN Process diagram can be displayed on the BPMN Collaboration diagram.