L-canceling (possibly officially termed a smooth landing) is a technique in both Super Smash Bros. and Super Smash Bros. Melee that allows characters to act faster than usual when landing in the middle of an aerial attack. L-cancelling is done by pressing a shield button 6 frames before landing during an aerial attack (the grab button also works because of its unique properties).
 In Super Smash Bros.
Better known as Z-cancelling as the Z button is the shield button, L-cancelling in Super Smash Bros. causes the character's regular landing animation to play instead of the air attack's landing animation, reducing their lag to 4 frames. Compared to lag intervals in the 20-30 range, this can allow incredible attack speed when combined with techniques such as double jump cancelling, resulting in shield break combos.
 In Super Smash Bros. Melee
L-cancelling in Melee causes the air attack's landing animation to play at double speed, cutting the lag time in half (rounded down). While not as potent as the previous game, the decrease in lag is significant enough to make some characters' L-cancelled air attacks better than comparable ground attacks; characters with more aerial landing lag such as Bowser or Ganondorf are considered the better abusers of the technique.
 In Super Smash Bros. Brawl
L-cancelling is not present in Brawl for unclear reasons. One theory is that, like tripping, L-cancelling's removal was to shift the game's focus away from competitive depth towards casual accessibility. The lack of L-cancelling acts as an indirect nerf to characters that have longer air attack lag times and/or low jumps (making it easier to land while attacking).