McNair is a small lunar impact crater on the far side. It lies within the double-ringed Apollo basin, inside the eastern part of the interior ring. It has partly merged with the crater Jarvis, and the two share a common rim. To the south lies Borman. (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.