Grapple canceling is a technique available to Samus, Link, Toon Link, and Lucas (the characters whose grabs are grapples) in Super Smash Bros. Brawl. The technique allows a midair grapple to be canceled, with no landing lag.
The easiest way to grapple cancel is to short hop, then press the grab button on the way down. If the character has a midair grapple move, it will extend quickly, lightly damaging those who touch it. Upon landing, there will be no lag, and any other move can be performed immediately.
Grapple canceling is most useful with Samus, as her aerial Grapple Beam ("zair") comes out quickly, has a long range, and has decent stun time on it. Samus can also short hop a Homing Missile and start her zair upon completion of the Homing Missile, canceling when it hits the ground. This technique is useful for pressuring, approaching, and stopping approaches.