Mees is a crater on the far side. It is located in a part of the lunar surface that is sometimes brought into view of the Earth under conditions of favorable libration and illumination. Even at such a time, however, this feature is seen from a very low angle and little detail can be perceived. This crater lies in the northern edge of the huge skirt of ejecta that surrounds the Mare Orientale impact basin. (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.