Perhaps Groupgroup dynamics
Definition: the interactions that influence the attitudes and behavior of people when they are grouped with others through either choice or accidental circumstances. Based on the Random House Dictionary
Or with a negative connotation deindividuation
Definition: Deindividuation is a concept in social psychology that is generally thought of as the loss of self-awareness1 in groups, although this is a matter of contention (see below). Sociologists also study the phenomenon of deindividuation, but the level of analysis is somewhat different. For the social psychologist, the level of analysis is the individual in the context of a social situation. As such, social psychologists emphasize the role of internal psychological processes. From Wikipedia, the free encyclopedia