Auto-canceling is the act of landing during the beginning or ending frames of an aerial attack, thereby circumventing the landing lag that would have occurred had the character instead landed during the middle of that attack's animation.
Auto-canceling an attack produces no more landing lag than a regular landing from an ordinary jump (of which the landing lag tends to be around 4-6 frames, a very short amount of time), whereas landing during the middle of an aerial attack almost always results in a significant delay before the character can act (raise a shield, jump, dodge, etc.) again. Most aerial attacks can be auto-cancelled during both the first few frames and the last few frames of the attack's animation; however, some attacks cannot be auto-cancelled at the start, at the end, or even at all. Each individual aerial attack for every character has a specific auto-cancelling window (or lack thereof) that must be memorized and practiced.
Auto-canceling can be very beneficial to players using characters with laggy aerial attacks, as this can reduce the amount of landing lag produced, and create more time for the character to act, potentially avoiding being punished during the move's landing lag. Precise auto-canceling of aerials is also frequently needed for performing followups and combos, so as to leave less time for the opponent to react and escape.
In Super Smash Bros. and Super Smash Bros. Melee, though auto-cancelling is useful, it generally has no large impact on gameplay, since L-cancelling is effective on its own in reducing landing lag. A notable example is Ness's down/up aerial shield break which requires many inputs so the lack of needing to z-cancel makes the shield break significantly easier. Melee reduced the effect of L-canceling making auto-canceling more useful although jumps are shorter than they were in Smash 64 and auto-cancel windows are far less lenient across the board making a lot less aerials capable of auto-canceling in a short hop. Super Smash Bros. Brawl removed L-cancelling making auto-cancelling more important and useful. However, aerial attacks in Brawl generally have more lenient auto-cancel windows to partially compensate which is further compensated by falling speeds being much lower than in Melee. A lot more aerials can be auto-cancelled in a short hop in Brawl compared to Melee because of these changes. In Super Smash Bros. 4, L-cancelling continues to be absent, and aerials overall have slightly increased landing lag and later auto-cancel windows, hindering aerial approaches and enforcing a heavier reliance on grounded combat.
In Super Smash Bros. Ultimate, however, since the landing lag on moves has been altered and substantially reduced across the board, aerial approaches have become safer than previously. Aerials are also considerably weaker when performed during a short hop. Because of this, auto-cancelling isn't as useful as it was in Smash 4.
The following characters' respective moves have notable auto-cancels.
List of characters who can auto-cancel all aerials in a short hop
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