Self-destruct
A self-destruct (abbreviated "SD") is the name for a "suicide" in Super Smash Bros. Melee and occurs when a character dies on his or her own without offensive interference by an opponent. (Interference by environment damage, however, such as cars, can still cause a self-destruct). Self-destructs carry various penalties in the different game modes. In Time mode, self-destructs subtract one point by default from a player's score; this penalty can be changed to zero or two points. In Bonus mode, the player's score is lowered by 500 points.
Killing a teammate also counts as a self-destruct.
Self-destructs are a lot more difficult to get in Super Smash Bros. Brawl, as various KOs that would have been a self-destruct in Melee count as regular KOs in Brawl.
