A peer is a person's equal. The U.S. Constitution guarantees criminal defendants a "jury of one's peers," which means an impartial group of citizens from the judicial district (e.g. county) in which the defendant lives. However, jurors are not required to be ethnically, educationally, economically or sexually the same as the defendant, although in some jurisdictions attempts are made to meet those criteria.
In the computer age, peer has also become used to refer to an individual computer. In pa peer-to-peer network of computers, the computers are linked directly to eachother, rather than through an intermediary server computer.