Roles describe the relationship between a person and an organization. A person can have multiple roles at the same time; and for every organization type, a different set of roles is available. For example, a person can have the role "professor" in a faculty and the role "group leader" in a research group.
Roles are time-controlled, so they have a start date and an end date. Access permissions, milestones and other information are automatically assigned to people based on their roles.