Suicide Black
Black will do anything to win. - common MtG saying
The fine art of ripping your own arm off and beating your oppponent to death with it.
A (black, of course) MTG Deck in which the player will sacrifice copious amounts resources (mainly life) in order to win. Often times the engines that win the game for said player are quite capable of killing them if the game does not end soon enough or if they they are beaten down, hence the term Suicide.
If you're asking, "Why the hell would I ever want to play a deck like this?", the answer is that you like to live life on the edge. Also there's a reason the cards you're playing are killing you; they're fucking powerful and usually game-defining. Also you're playing disruption, preventing your opponent from most effectively taking advantage of your vulnerabilities and/or stopping his deck from what it wants to do.
Take for example Thoughtseize. This card is the single most powerful discard spell in the game for its mana cost, and it will ruin strategies from the very first turn of the game if you're lucky enough to open with it. Consecutive Thoughtseizes will not only make your opponent cry tears of blood but also give you a significant edge in the following game turns. However, misuse it or whiff with it, and you've basically just Shocked yourself. If you do cast four of these in a game (you trollish devil, you), you're paying 8 life to do so. Ouch. But again, you live life on the edge.
Another staple Suicide Black card is Bob, A.K.A. Dark Confidant. To the untrained eye, this card seems very mediocre if not outright bad. However, when your deck is built around him, you will quickly discover that he is an insanely powerful draw engine, albeit one that requires some finesse. He's much more complex than a Howling Mine or a Phyrexian Arena but offers incredible raw power for his meager 1B Mana Cost and solid 2/1 beatstick body.
Another thing that makes this deck explosive is rituals. Sacrificing card advantage for a little tempo.
The real question you have to ask, however, is how you're going to actually win. You're losing tons of life every turn, and eventually you're going to die. The most straightforward and consistent strategy is straight up Aggro. Black has a ton of cheap, powerful bodies with a "downside", typically life loss. Unlike other straight up aggro decks you have great removal (Black's defining feature), disruption (Thoughtseize and brethren, maybe some land destruction), and insanely powerful, cheap draw engines that Red and Green wish they had (Necropotence when legal, Phyrexian Arena, Bob). Of course your downside compared to them is that you're on a clock from constantly draining yourself, but some cards can help mitigate this. If you do add these cards you have to consider how they're going to impact how quickly your deck wins and if they're more powerful than other options that hurt you.
If you play Suicide Black be wary of Burn and Enchantment based decks. Burn loves the fact that you pay life every damn turn to do things, and Black has no way to deal with Enchantments effectively. Luckily Enchantment decks aren't exactly the bee's knees but some people adore them, so be considerate of the meta you play in. Burn is also less common than Red Deck Wins in tournaments, but is much more common in casual play.
Just always remember; the only life total that matters is 0. If you're not at 0, you're not dead. And even then you may not be dead but we don't use those cards in Suicide Black. We're just too manly. Sure we might use Abyssal Persecutor but that stops its controller's opponent(s) from being dead at 0 life (or dead for other reasons), at least as long as its on the battlefield. And black has no shortage of ways to sacrifice its own creatures (at least in eternal formats), so that isn't much of a problem.
tl;dr: The fine art of ripping your own arm off and beating your opponent to death with it.