Why is it called a FULL BRIDGE RECTIFIER?

FULL: It's a FULL bridge rectifier because it rectifies the full wave of an AC signal.
BRIDGE: It's a full BRIDGE rectifier because this orientation of circuit (two parallel branches, bridged by a third) is called a bridge.
RECTIFIER: It's a full bridge RECTIFIER because the squiggly AC voltage is fixed and set to a constant DC voltage.

This video briefly and clearly explains in non-technical terms what the purpose of a full bridge rectifier is, and how it works.