1. a group lacking interdependence, group cohesion, structure, and other characteristics typically found in social groups. An example is a group of people disembarking from a bus.

2. a type of zero-history nominal group assembled and studied in the minimal intergroup situation. It has been found that individuals in such groups respond in biased ways when allocating resources to ingroup and outgroup members, even though the groups are not psychologically or interpersonally meaningful. [introduced by Polish-born British social psychologist Henri Tajfel (1919–1982)]