Smashpedia:Article of the Week/2007-18

Directional influence (usually abbreviated DI, which can be used as a verb) is the control the target of an attack has over its trajectory in Super Smash Bros. Melee. Each attack sends its target in a particular direction, depending on the attack itself and on the target's weight and falling speed; DI can be used to alter, but not completely change, this trajectory. This change, however, can be vital to surviving high-power attacks such as Fox's up smash, and for escaping combos such as Jigglypuff's Space Animal Slayer.

The player can DI by pressing the control stick in any direction during or just after being hit by an attack. There are three types of directional influence: regular DI, smash DI, and automatic smash DI. The type of DI changes depending on when the player presses the control stick. (read further...)