Suicide Black, often simply called Sui, is an archetype of deck and share similarities with Sligh or other aggressive Red decks.  However, the primary and usually only color in the deck is, appropriately, Black. Decks of Suicide Black flavor usually use cheap, aggressive black creatures such as Phyrexian Negator, which usually come with a significant drawback to balance the card. Suicide Black would attempt to end the game before these drawbacks would have any significant effect on the game.
Suicide Black decks were more popular when Black still retained short-term mana-boosting cards such as Dark Ritual, which have since been moved into red as well as significantly weakened. Suicide Black decks would also usually employ a significant amount of Discard, e.g. Hymn to Tourach, as well as removal spells to keep the opponent from interfering with the game plan.