Chaffee is a lunar impact crater that is located in the southern hemisphere on the far side. It lies within the huge walled plain Apollo, and is one of several craters in that formation named for astronauts and people associated with the Apollo program. This basin is a double-ringed formation, and the crater Chaffee is situated across the southwest part of the inner ring. The ridge from this ring extends northward from the northern rim. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.