Cavalerius is a prominent lunar impact crater that lies on the western edge of the Oceanus Procellarum lunar mare on the west part of the visible Moon. It nearly joins the northern rim of Hevelius to the south. The rim is high, rising to over 3 kilometers in places. There are clefts in the northern and southern parts of the rim and inner walls. (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.