Grissom is a lunar crater that lies on the far side. It is located just to the south of the huge walled plain Apollo, and to the northeast of the crater Cori. The rim is eroded in places, particularly along the northeast where a pair of small craters lie along the sides. There is a clustering of small craterlets located to the south of the crater midpoint. (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.