Guard is an ability that Sora can use in Kingdom Hearts and Kingdom Hearts 2.Roxas can also use it.It is one of the most useful abilities in both games.
A variant of this is Dodge Roll,used in Kingdom Hearts and Kingdom Hearts 2: Final Mix+.
It can not only deflect enemy attacks,but it also shoots back projectiles (Fat Bandit's fireballs,Fortuneteller's icicles,ect.)
Also,some enemies do or have things similar to Guard (ex.Large Body's stomach).