There is widespread agreement in the object community that the concept of role is important for object modelling, but little agreement about what is to be understood by a role. In this paper, we present a new definition for the concept of role in the context of ISOs RM-ODP Foundations for object modelling. We show that the concept of role is similar to that of interface, but that there important differences between these two concepts. We also provide definitions for concepts, related to the role concept, that may also be called roles: role type and role object type. We then make the case for our definitions, showing that they are largely compatible with assertions that exist in the literature about roles.