What are "peers"?
Peers are any persons or group of people who have a close but generic relationship to one another. For instance, people of a similar age group, people in the same circle of friends, people in the same class, people in the same counseling group, people in the same volunteer group, people at the same workplace, people in the same family, etc. In order for a group to be considered a "peer group" we look for one or more of these commonalities. When we speak of teen peer pressure, peers generally refers to people in the same age group (12 - 19) who have one or more of the other relationships listed above in common. The other teens at your school, at your work place or in your social circle are usually what we mean when we talk about peers for the purposes of peer pressure.
What is peer pressure?
Peer pressure is a social force exerted by a group or powerful/admired individual within a group. It is generally a pressure to conform to a social norm within any given group. Not all peer pressure is bad. Social norms are a very important part of human interaction and group dynamics. Social norms are expectations that a group has of its members usually related to behavior. Since most social norms contribute to the smooth interaction of individuals within a society, peer pressure that promotes conforming to these norms serves a positive purpose.
When social norms become deviant or harmful or when the social norms in a group are radically different to the generally accepted social norms of a society then we consider them to be "bad". When most people think of peer pressure they are thinking of the pressure to conform to a deviant behavior set. Things like drug use, underage alcohol use, promiscuous sexual conduct, violent or aggressive acting out, or criminal behavior are examples of the negative peer pressure associated with teens.