McMath is an impact crater. It lies to the south-southwest of the prominent crater Jackson, and material from the ray system centered on Jackson lies across most. Farther to the south lies the crater pair of Zhukovskiy and Lebedinskiy. This is a worn, torn up, and eroded crater formation with several small craters along the rim edge. (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.