The Libero is the player that wears a different jersey than the rest of the team. They are the best passers, displaying quickness and accuracy.
The libero often subs in for the middle hitter (MB) and will play in the left or middle back positions. Liberos will play in one of these two spots because the majority of balls that come from the other side of the net go to these areas.
They sometimes can serve, but there are a few restrictions.