Glitch

A glitch is a programming error or quirk in software, usually originated from bad code to unused space in RAM. Glitches range from harmless to harmful, depending on what it effects. Glitches that are usually harmless could be beneficial to the player such as granting them extra lives or an "unlimited" amount of an item, etc. while harmful glitches could effect major parts of a game's code, rendering the game un-playable.