A glitch is technological "mistake" of sorts that can alter gameplay. They involve the game functioning in ways it was not programmed to act in. Glitches can be harmful, such as freezing the game, erasing save files, causing a level to be unplayable, or killing a player for no reason. Not all glitches are harmful; many can be utilized to improve gameplay and ever worked into strategies. Glitches can allow item use when it is not normally possible, entry into unfinished level zones, or even cheating to finish games better or faster.
Famous glitches in the Super Smash Bros. Melee include the Black hole glitch and the Yoyo/Jacket glitch (see the category for more). Techniques such as Wavedashing are not considered glitches, but more of an exploit of the game's physics.