- Were you looking for the definition of a Passive ability?
Passive is one of the possible "postures" of a pet. A passive pet will only attack mobs if its master gives it specific orders to attack. Otherwise, it will follow its master and ignore attacks on itself or its master. Other possible pet postures are Assist and Defensive.
One way to pull your pet out of a battle is to make it passive and run away, the pet will then follow out of the attacker's pursuit range.
"Passive mobs" are mobs with yellow nameplates and do not aggro when the player comes within close proximity.