Plana is a lunar crater that lies on the boundary. It is joined to the crater Mason to the east by a short stretch of rugged ground. Due north in the midst of the Lacus Mortis is the prominent crater Bürg. This is a crater with a slender outer rim that has been worn and eroded by impacts. (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.
