A peer is someone at your own level. If you are a 10th grader, other high school students are your peers.
Peer comes from the Latin par which means equal. When you are on par with someone, you are their peer. If kids your age are pressuring you to do something you don't want to do, that's peer pressure. In the sport of basketball, Michael Jordan was without peer, no one could equal his talent. When he switched to baseball, he found himself to be among peers again.