A Process describes a flow of Activities in an organization with the objective of carrying out work. In BPMN, a Process is depicted as a graph of Flow Elements, which are a set of Activities, Events, Gateways, and Sequence Flows that define finite execution semantics. Processes can be defined at any level from enterprise-wide Processes to Processes performed by a single person. Low-level Processes can be grouped together to achieve a common business goal. A Process is not a specific graphical object, but is rather a set of graphical objects.
A public Process contains Activities visible to external parties, such as Participants in a Collaboration.
A private Process includes other Activities that are not visible to external parties. The hidden Activities in a private Process are not modeled in the public Process. However, it is expected that instances of the private Process will appear to external parties as if they could be instances of the public Process. This means the private Process supports the public Process (it is expected that all instances of the private Process will be valid for the public one).