Buffer
The buffer is a mechanic in Super Smash Bros. Brawl and Super Smash Bros. 4, which allows players to successfully input actions up to 10 frames before they can actually be executed. Whenever a move is used in Brawl, a window of 10 frames is created at the end of every move and animation, in comparison to Melee's 0 frames. During this time, any input will be carried out the first frame possible as soon at the move or animation is finished. This is beneficial, as it allows the player to perform a move the instant another move or animation is finished, allowing them to respond as soon as possible with greater input accuracy; a feat which would otherwise require frame precision. Buffering is required in many damage-racking combos to minimize the opportunity for the opponent to escape.
However, there are also negative effects to buffering a move. Buffering may lead to unintentional inputs that carry out (e.g. attempting to buffer a jab nearby the ledge while shielding, which would result in using a neutral aerial off the stage). This kind of situation can be deadly to characters with laggy neutral aerials, such as Ike, whose recoveries do not provide enough vertical distance to recover after the attack ends.
In Melee, it is possible to shield buffer some evasive options by holding the C-stick together with a shield input. The character will then proceed to jump (if held upwards), spot dodge (if held downwards) or roll (if held sideways) at the first instant possible. There is also a grace period of 3 frames in which one can fast fall after the peak of any jump.
In Smash 4, it is not possible to buffer the following; any ledge option using the control stick, grab aerials, airborne item catches after an air dodge, Z-dropping items after an air dodge, and shield after dropping the input during the 10 frame period. There is also a hierarchy of moves that will come out when multiple inputs are pressed at the same time; special moves have the highest priority, followed by shields, attacks, jumps, and stick inputs, in that order. This hierarchy is the reason why buffering both a control stick input and a button input at the same time is impossible and thus, a common problem. For ledge options, ledge jumping has the highest priority, followed by ledge attacking and ledge rolling.
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