Peer Pressure- definition

Definition:
Peer pressure is influence that a peer group, observers or individual exerts that encourages others to change their attitudes, values, or behaviors to conform to group norms. Social groups affected include membership groups, in which individuals are "formally" members (such as political parties and trade unions), or social cliques in which membership is not clearly defined. A person affected by peer pressure may or may not want to belong to these groups. They may also recognize dissociative groups with which they would not wish to associate, and thus they behave adversely concerning that group's behaviors.^{[citation needed]}
Peer pressure is most commonly associated with youth, in part because most youth spend large amounts of time in schools and other fixed groups that they do not choose and are seen as lacking the maturity to handle pressure from friends. Also, young people are more willing to behave negatively towards those who are not members of their own peer groups.^{[citation needed]}
Peer pressure can also have positive effects when people are pressured toward positive behavior, such as volunteering for charity or excelling in academics or athletics, by their peers. This is most commonly seen in youths who are active in sports or other extracurricular activities where conformity with one's peer group is strongest
http://en.wikipedia.org/wiki/Peer_pressure