Self-destruct

Self-destruct (also known as SD) is when a player kills himself. Most often, a SD is involuntary, and almost always implies human failure, like a bad-timing recover move or to step on a mine. But, also a self-destruct can be voluntary, like in Time mode, when a player with high damage self-destructs for reborn at 0% damage and avoid any other rival to KO him; but this is considered a dirty strategy. Melee (and presumably Brawl too) provides a way (in advanced options menu) to discount more points for players who SD.