Oppenheimer is a large lunar crater that lies on the Far side. It lies along the western outer rampart of the immense walled plain Apollo. Nearby features of note include the dark-floored crater Maksutov to the southwest, and Davisson to the west-southwest. The latter intrudes into the eastern rim of Leibnitz, a feature about 20% larger than Oppenheimer. (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.