Expose Weakness

Expose Weakness, also known as Guard-Off, is a recurring Blue Magic spell.

Final Fantasy V
Guard Off (called Off Guard in some translations) is a Blue Magic spell that lowers enemies' Defense. It can be learned from Page 256.

Final Fantasy Tactics Advance
Guard-Off lowers Defense and Magic Resistance of a unit for the duration of a battle.

Final Fantasy Tactics A2: Grimoire of the Rift
Expose Weakness is a Blue Magic spell learned from Drakes that reduces a unit's Defense and Magick Resistance.