This document defines and provides examples of different types of reference groups, including membership reference groups and disclaimant reference groups. It then describes several specific types of social groups, including peer groups, cliques, households, communities, gangs, mobs, posses, squads, dyads, triads, teams, in-groups, and out-groups. For each type of group, a brief definition or example is given to explain the nature and typical characteristics of that social grouping.