In martial arts terminology, to trap is to check, or immobilize an opponent's arm to prevent them from hitting you, or blocking your next punch. Basically it's pressing on the person's arm just above or below the elbow to keep it at an angle from which it is impossible to hit you. This is not the same as blocking, which is done as a reaction to an incoming punch, but rather is done proactively whether the opponent is attacking or defending. In Jeet Kune Do's Five Ways of Attack, trapping falls into the HIA, or Hand Immobilization Attack.