Milichius is a bowl-shaped lunar impact crater that is located in the northern part of the Mare Insularum. To the southeast is the slightly larger Hortensius, a similar formation. Further away due east is the prominent and well-known Copernicus. Just to the west is a typical lunar dome designated Milichius Pi that has a tiny craterlet at the peak. (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.