A role is a functional relationship which an agent has with one or more agents or resources.
Agents often serve roles in projects and collectives. (Projects and collectives are resources.)
Each role has one or more accountabilities and authorizations, although they often remain undefined. Many roles also are exclusively assigned, and have prerequisite requirements.
Complex ongoing roles are often referred to as posts, positions or occupations. (Note that position is defined much more generically in MOT.)