McAdie is a flooded lunar crater that is located along the northeastern edge of Mare Smythii, on the far side. It lies just to the southwest of the larger, flooded Babcock. During periods of favorable libration and illumination, this area can be viewed from the Earth, although it is seen from the edge and not much detail can be discerned. The interior of this crater has been submerged by basaltic lava, leaving only a portion of the rim projecting part way out of the surface. (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.