In Kingdom Hearts, Counterattack is a combat ability that costs 2 AP to equip. Successfully counterattacking restores some of Sora's MP. It also always inflicts a Critical Hit. Counterattack can also be deflected, and it can be performed from any form of normal recoil, from both an attack being deflected or successfully guarding. If Sora is wielding a Keyblade that's listed as being "difficult to deflect", he cannot be knocked off-balance when blocking/parrying an attack that would do so otherwise, and will instead react with normal recoil. This allows him to perform Counterattacks more often.
Kingdom Hearts Final Mix