Roles, Responsibilities, Collaborators
An object is an implementation of one or more roles;
a role is a set of relatedresponsibilities;
and a responsibility is an obligation to perform a task or know information.
A collaboration is an interaction of objects or roles (or both).
(origin: Wirfs-Brock and McKean in [Wirfs-Brock03])
(src: Book: Growing Object Oriented Software, Guided By Tests - Steve Freeman & Nat Pryce)