Participant
A Participant is an entity participating within a bounded context such as a Formation, Community, Activity, or other governed arrangement.
Specification-sourced: quoted from the governing specification, pending the applicable specification-owner approvals. The specification controls.
In plain words
An Organization does not become a Participant merely because it exists in the network. The same entity may participate in many contexts, say a mill in two different Formations, while keeping one durable identity.
What it is not
Participant ≠ Subject
A Participant takes part in a bounded context; a Subject is merely what an expression concerns, so a watershed a Formation aims to improve is not thereby a Participant. Subject Is Not Participant · Subject Model (source: 02 §3.3)
Participant ≠ Actor
Participating means taking part in a bounded context, while acting means being responsible for performing an action; one Person may be both at once. Subject Is a Role · Concept Paper (source: 01 §3.1)