1. In SSBM
pressing the L button just before landing after doing an A move in the air. Results in an extremely fast recovery, so that another move can be done after landing without delay.
2. Among SSBM
players, a term used when telling someone to try to undo something, or to try to stop doing something.
1. Because I L cancelled, I was able to hit the fox player before he recoverd from the previous hit.
2. Person 1: oh shit! I accidentally sent my girlfriend a text message saying I want to break up!
PErson 2: You better L cancel that shit!