One side of the moon is permanently turned away from the Earth due to tidal forces creating what is known as “tidal-lock." To better understand our celestial companion, we launched dual space sensor satellites on a reconaissance mission, GRAIL:
Because the moon doesn’t rotate on its axis, the far side receives no relief from meteors and other space debris travelling in its direction. The result is the cratered surface you see below.
The far side as imaged by the Apollo 16 spacecraft:
Part of the near side is on the left in this image.