Billy (Moon)

Named after Jacques de Billy - French mathematician (1602-1679).

Billy lies to the southeast of the similar-sized crater Hansteen, and west-southwest of the flooded Letronne. The portion of the rim remaining above the surface is narrow and low, with a thin inner wall. Only a few tiny craterlets mark the interior. (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.