The one hemisphere of the Moon that is always facing away from the earth. The rotation of the moon matches its revolution around the Earth and hence it keeps one side always facing us. This has partly due to the fact that the center of mass of the Moon is off center and facing towards Earth's gravity. Over time Earth's gravitational pull slowed down the Moon's rotation to the equilibrium it is in today.

The far side is also often mistaken to be the dark side of the moon even though it receives equal amounts of sunlight as the Earth side. This is a good reflection of human psychology as well.