1. in general, any group to which one belongs or with which one identifies, but particularly a group judged to be different from other groups (outgroups).

2. a group characterized by intense bonds of affiliation such that each member feels a sense of kinship and some degree of loyalty to other members by virtue of their common group membership. Also called we-group. [defined in 1906 by U.S. sociologist William G. Sumner (1840–1910)]