Galois is a large lunar crater on the far side. Features of this class are commonly termed walled plains, due to their appearance and dimension. It is located just to the southeast of another huge walled plain, Korolev, a formation nearly double the diameter. Several hundred kilometers due south is another enormous feature, Apollo. (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.