Last Full Moon.
Tidal forces between Earth and the Moon have slowed the moon's rotation so that the same side is always facing the Earth. The other face, which is never visible from the Earth in its entirety (18% of it can be seen under some conditions, see Tidal locking), is therefore called the "far side of the Moon".
The far side should not be confused with the "dark side" (the hemisphere that is not illuminated by the Sun at a given point in time), as the two are the same only during a full moon.