Peer pressure (or social pressure) is influence a peer group, observers, or an individual exerts that encourages others to change their attitudes, values, or behaviors to conform to those of the influencing group or individual. Social groups affected include both membership groups, in which individuals are "formally" members (such as political parties and trade unions), and cliques in which membership is not clearly defined. However, a person does not need to be a member or be seeking membership of a group to be affected by peer pressure. One may also recognize dissociative groups, with which one wishes to avoid associating, and thus behave counter to that group's norms.