Glitches (or bugs) are oversights in the making of a game that lead to unexpected results, and are exclusively a flaw of the game's software. These can be triggered by the player accidentally or purposely, and can be beneficial, harmful or harmless. Some glitches are abused in order to successfully complete otherwise impossible challenge runs.
There are four pages that list glitches in games in the series, organized by game:
It is recommended that you read the glitch notes before attempting any of these glitches, or before adding your own.