Named after Mark Muir Mills - American physicist (1917-1958).
Mills is a small crater that lies on the far side. It is located to the northeast of Henderson and to the south of Kohlschütter. This is an undistinguished impact crater that is roughly circular in form, with a slight outward bulge to the northwest. This bulge may be due to the merger of a smaller impact with the 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.