Conversation so far:
what is on the far side of moon
The far side of the moon has one of the largest craters in the Solar System, the South Pole Aitken basin.
what is the far side of the moon's terrain like
The far side of the moon's terrain is rugged with a multitude of impact craters and relatively few flat lunar maria compared to the near side.
what percent of the far side of the moon is visible from earth
About 18 percent of the far side of the moon is occasionally visible from Earth due to libration.

Question: what is libration
Self-contained rewrite: what is libration in lunar astronomy