XII Zone out glitch is a glitch in Final Fantasy XII that tricks the game into thinking a dead monster has not been spawned yet, and thus respawns it. The glitch activates when an enemy is killed, but the character crosses a zone line before the EXP and LP amounts appear on screen.
The EXP and LP gained from killing the enemy are earned, but the monster will respawn (assuming its spawning conditions are met again) when the character crosses immediately back into the area they just left. This glitch is used most commonly to Chain together Rare Game, without having to zone away twice between each kill.
Exploitation of this glitch can also cause a very high battle chain, resulting in a larger amount, and increased frequency, of drops. This glitch is commonly used on the rare monsters Dustia and Helvinek; Dustia by low leveled characters in the beginning of the game to quickly amass large amounts of EXP, LP, and gil (from selling the Books of Orgain Dustia drops), and Helvinek to procure multiple sets of Grand Armor.