Auto-canceling

Auto-canceling is the act of landing during the beginning or ending frames of an aerial attack, which will make the player go into their normal landing animation from a jump (of which the landing lag tends to be around 2-6 frames depending on the character, a very short amount of time), thereby circumventing the landing lag that would have occurred had the character instead landed during the middle of that attack's animation which can be a significant amount of time depending on the aerial.

Technical explanation
When an aerial is performed, it will not immediately make the player go into their aerial landing animation if they land. Instead, they will enter their normal landing animation and the game has to call for a command in order to enable the aerial to enter its landing animation. The period of time before this command is called for is known as the initial auto-cancel window. When this command is disabled, the character will then enter their normal landing animation for the rest of the aerial's duration. This is known as the late auto-cancel window. If an aerial does not have an initial auto-cancel window, the character will enter their aerial landing animation as soon as the aerial begins (if they land). If an aerial does not have a late auto-cancel window or if the late auto-cancel window occurs after the animation has ended, the character will enter their normal landing animation once the aerial's animation has finished (interruptibility does not affect this). If the command for the aerial to enter landing lag is never called for, the aerial will always auto-cancel although this is extremely uncommon.

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 do not have an initial auto-cancel window, a late auto-cancel window, or even both. Each individual aerial attack for every character has a specific auto-cancelling window (or lack thereof) that can be memorized and practiced. Late auto-cancel windows are also significantly more beneficial as almost all initial auto-cancel windows end before an aerial's hitbox comes out making them irrelevant in most situations.

Applications
Auto-canceling can be very beneficial to players using characters with laggy aerial attacks (granted they have an early enough late auto-cancel window), 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.

Differences between games
In Super Smash Bros., auto-cancelling generally has no large impact on gameplay, since Z-cancelling has the same effect, although some moves do have extremely lenient auto-cancel windows. A notable example is 's down/up aerial, which will always auto-cancel. These moves can be used for shield breaks, which requires many inputs, so the lack of needing to Z-cancel makes the shield break significantly easier. All aerials except for 's up and down aerials are capable of auto-canceling in a short hop.

Super Smash Bros. Melee reduced the effect of L-canceling (now only halving the landing lag as opposed to giving the character their normal landing), making auto-canceling more useful, although jumps are shorter than they were in Smash 64 due to gravity being increased across the board, 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-canceling, making auto-canceling more important and useful, as while numerous aerials have lower landing lag, none of them had their landing lag reduced enough to completely compensate for the removal of L-canceling. Aerial attacks in Brawl generally have more lenient auto-cancel windows, which is further compensated by gravity/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 with far fewer aerials losing their ability to auto-cancel in contrast.

In Super Smash Bros. 4, L-canceling 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. While some aerials gained the ability the auto-cancel in a short hop, a majority lost their ability to do so either because of their worse auto-cancel windows, the character's lower short hop or both. An additional change is that when an aerial or a special is auto-canceled, the player will always go into their hard landing lag animation, regardless of their falling speed. In Brawl, auto-canceling does not affect whether the player gets a soft or a hard landing.

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 with these changes overall making auto-canceling less useful depending on the aerial. However, many aerials (e.g. 's down aerial) have improved auto-cancel windows enabling them to properly auto-cancel in a short hop although naturally, the opposite is also the case with some aerials (e.g. 's forward aerial) and some characters are now unable to auto-cancel certain aerials due to their higher gravity/falling speed reducing the height of their short hop (e.g. 's forward aerial). Characters still always enter their hard landing animation when auto-canceling a move.

Notable examples
The following characters' respective moves have notable auto-cancels.

Smash 64

 * His forward aerial's initial auto-cancel lasts 19 frames however, the move's hitboxes are active from frames 8-15. This means that the move auto-cancels while its hitboxes are active removing the necessity to Z-cancel unless DK lands during a certain period (frames 20-35) after he has already performed the move. Forward aerial is a fast and powerful meteor smash with solid combo potential. In later entries up until Ultimate patch 2.0.0, the move could no longer auto-cancel at all.
 * His up aerial and down aerial will always auto-cancel. This allows him to get easy shield breaks along with his DJC (double jump cancel) as well as start long combo strings since his dair has one of the longest lasting hitstun in the game.
 * Pikachu's up aerial will always auto-cancel like Ness'. Its large disjointed hitbox and coverage behind and in front of Pikachu make it an effective approach option and defense option. It also combos into itself or into finishing moves such as Pikachu's back aerial. No aerials in subsequent entries can auto-cancel for their entire duration.

Melee

 * His up aerial's large auto-cancel window allows it to combo into itself, especially against fastfallers.
 * Back aerial auto-cancels when done at the very start of a short hop. The large disjoint on the move's sweetspot makes this an effective way to wall out approaching opponents. Interestingly, Falco's down aerial can be autocancelled for movement purposes. When on one of Yoshi's Story's side platforms, Falco would normally have to fullhop to reach the top platform. This would be slow and cumbersome, making techchases or combos that end on the top platform much harder. However, his down aerial shifts his environmental collision boxes far enough up that, if timed properly, Falco can short hop off the side platform, down aerial, and autocancel the aerial on top platform. This is considerably faster than the alternatives and enables Falco to further extend punishes.
 * Neutral aerial auto-cancels before its hitbox ends which can make the move frame positive on shield if executed perfectly.
 * Neutral aerial's large hitbox and long duration make it an effective approach option, especially out of a dash dance. This was retained in Brawl but neutral aerial's auto-cancel window was made far worse in later entries.
 * All his aerials auto-cancel in a short hop. His down aerial auto-cancels as long as the hitbox is not active, making the move frame safe on shield if executed perfectly. This auto-cancel window was retained in Brawl.
 * Forward aerial can autocancel almost immediately after it is initiated, doing so from frame 11 onward, making it one of the safest aerials in the game. It retains this trait in subsequent Smash games although it auto-cancels one frame later in Brawl due to the hitboxes' longer duration.

Brawl

 * All of his aerials auto-cancel in a short hop. His down aerial's meteor smash has good combo ability, and his Knee Smash can be used to approach and KO.
 * Back aerial has a very lenient auto-cancel window with Fox being able to hit even the shortest characters with it and still auto-cancel the back aerial. Back aerial is a powerful semi-spike making it a good move to use near the ledge.
 * Approaching with his down aerial meteor smash is known as Thunder-stomping, and it has excellent combo ability and KO power as well. Up aerial is also a decent KO option.
 * His powerful back aerial is useful for both approaching and KOing although it is his only aerial which can auto-cancel in a short hop.
 * Back aerial auto-cancels as soon as its hitbox ends. This should not even occur as the move should have 4 frames of lag before it can auto-cancel but because back aerial's auto-cancel window is listed in the move's script before the command to remove the late hit's hitboxes, it makes the late hit linger for 4 extra frames and removes the hitboxes once the move can auto-cancel. Back aerial is Dedede's best approach option besides his grab and its unintentionally lenient auto-cancel makes his already amazing back aerial that much better.
 * All of his aerials auto-cancel from a short hop but more notably, he can perform two forward, up or down aerials in a short hop and he will still auto-cancel them making them strong approach tools on the ground especially forward aerial.
 * All of his aerials auto-cancel in a short hop. Most notably, his forward aerial's long range and autocancel window give it great utility in relieving pressure, approaching, and comboing.
 * Her forward aerial is a powerful spacing tool and it auto-cancels as soon as the hitbox ends. Her back and down aerials also share this trait.
 * All of his aerials auto-cancel in a short hop. Neutral, back and down aerials all have extremely lenient auto-cancel windows and the latter two can be used for recovering.

Smash 4

 * Back aerial's range and power make it a useful for approaching, pressuring, starting combos, and KOing.
 * Both up aerial and down aerial have long hitbox durations and auto-cancel immediately after their hitboxes cease, with the former doing so in a short hop, making them useful for disrupting opponents' approaches and starting combos.
 * Back aerial has one of the most lenient auto-cancel windows in the game, with only a 7 frame window where it will suffer any landing lag. While it does not auto-cancel as reliably as its Brawl counterpart due to Fox's higher falling speed and it is weaker, it is even safer on shield in Smash 4 due to the general increase to shieldstun/shield damage.
 * Forward aerial is a good combo move and spacing tool, and just like Brawl, back aerial is quick and one of his best KO moves.
 * While not quite as effective as his previous back aerial, back aerial's range and power make it arguably his best KO move.
 * Back and up aerials can autocancel in a short hop. Up aerial has a large initial autocancel window and autocancels early, and is an effective juggler due to its low knockback and angle. Back aerial comes out faster than all of his aerials and is his strongest aerial, making it one of his best KO moves.
 * As with all previous entries, all aerials auto-cancel from a short hop although unlike Brawl, he cannot perform two up or down aerials in a short hop and auto-cancel them. Forward aerial is good combo move, and back aerial is one of his better KOing options.
 * Up aerial is great combo move and can lead into Super Jump Punch. Back aerial can wall of pain due to its speed.
 * Back aerial is his strongest aerial, and has a significant auto-cancel window on startup.
 * Up aerial is very fast and is great for juggling.
 * While his back and down aerials have noticeably worse auto-cancel windows, his neutral aerial has a large hitbox, and is effective at approaching, relieving pressure, and starting combos.
 * Forward, neutral, and back aerials auto-cancel in a short hop. Specifically, forward aerial is one of her best moves due to its abnormally lenient autocancel window, being effective for approaching, pressuring, comboing, and KOing at very high percentages.
 * Up aerial has a large auto-cancel window coming immediately after its hitboxes cease, making it a low risk move. It is great for combos and KOing near the upper blast zone. Back aerial is Sonic's main KO move and forward aerial is good for edgeguarding. Down aerial auto-cancels after a double jump up special or an up special from the top Battlefield platform, allowing Sonic to land surprise KO's and setup Lock combos.

Ultimate

 * Neutral aerial autocancels whenever it doesn't have a hitbox active. This starts from frames 1-9, making it one of the best A-landing options in the game. Afterwards it autocancels from frame 27+, making it a premier combo starter for the character as well.
 * Fox's up air can autocancel out of a shorthop, allowing it to combo into itself 3-4 times if hit below a platform.
 * Down air was buffed in patch 6.0 to autocancel out of a short hop, opening up significant combos for it.
 * Luigi can auto-cancel all of his aerials (except grab aerial which doesn't have an auto-cancel window) in a short hop, can auto-cancel all except neutral aerial in a short hop fast fall, and can perform two forward or up aerials in a short hop and auto-cancel the second one.
 * Unlike the previous titles, Pikachu's back air autocancels out of a short hop, allowing it to combo into itself.
 * Squirtle's back air and down air autocancel out of a shorthop, most notably allowing back air to combo into itself, and down air to combo into grab/itself.
 * All of Terry's aerials have exceptionally wide autocancel windows. Down aerial is notable for allowing him to A-land on Pokémon Stadium 2 platforms, which he otherwise cannot even land on from a full hop.
 * Wario's back air can autocancel out of a short hop, allowing very safe and threatening ledge pressure.
 * Wolf's back air is notorious for having an especially large autocancel window, not only can it be done out of a short hop, but it can be delayed significantly, this grants Wolf a very noncommittal kill option.

List of characters who can auto-cancel all aerials in a short hop
* As of version.

** As of version.

Trivia

 * The forward airs of in Melee, and of  and  in Brawl, SSB4, and Ultimate before patch, cannot be auto-cancelled as soon as they should. By exploring the code of the games and looking at the underlying properties of the moves, it has been discovered that the developers had intended for auto-cancelling those moves to be possible; however, due to a minor error (the accidental use of the wrong type of timing function), those moves auto-cancel significantly later. In Donkey Kong's case, his forward aerial should auto-cancel on frame 56, but it instead auto-cancels on frame 85 in Melee and Brawl and frame 78 in SSB4 (although in theory, it auto-cancels on frame 60 in Melee and Brawl and on frame 56 in SSB4 due to forward aerial's animation length). In Ganondorf's case, his forward aerial should auto-cancel on frame 36, but it instead auto-cancels on frame 55. In Brawl, this also negatively affects his forward aerial's interruptibility, giving it 10 more frames of ending lag than it should have.
 * is the only character in SSB4 who cannot auto-cancel any of their aerials at all, due to his auto-cancel windows on all of his aerials being programmed after they can be interrupted while their animations have not completed (his forward aerial has the least severe case, as unlike his other aerials, it can auto-cancel a decent while before the animation has finished and has a strict 3 frame window to be auto-cancelled in a full hop). However, this allows him to cancel an aerial attack's ending lag with another action (jumping, aerial, airdodge). also exhibits this trait with his up aerial in Brawl, and multiple other aerials in SSB4 (such as 's forward aerial and 's up aerial) also share this trait. All aerials with this trait had their auto-cancel windows fixed in Ultimate patch 2.0.0.
 * Luigi is the only of the 12 veterans who can auto-cancel all of their aerials out of a short hop in every game.
 * Link is the only veteran who is unable to auto-cancel all their aerials in a short hop in Smash 64, as his up and down aerials have a very long hitbox duration, causing them to have strict auto-cancel windows.
 * in Ultimate is both the only DLC character and the only third-party character in the entire series who can auto-cancel all of their aerials in a short hop.