Originally a sub-genre of thrash metal pioneered by Possessed but made better by other band Death and Morbid Angel. The genre involves highly distorted, fast-paced guitars, blast beating drums and vocals that are unintelligible or make lyrics hard to understand.
Today there are several sub-genres of death metal. Technical death metal focuses on having complex leads and song structures. Brutal death metal is all about pushing death metal past the boundaries in speed and aggression. Melodic death metal has higher pitch vocals and melodic guitars. Deathgrind fuses the complexity of death metal with the speed and aggression of grindcore. Death/doom fuses the double bass drumming and growling vocals of death metal and the slow tempo and pessimistic mood of doom metal. And deathcore mixes the gore of death metal with the core of metalcore to get a genre even more gay and worse than metalcore.
Traditional death metal: Death, Morbid Angel, Deicide
Technical death metal: Cryptopsy, Psycroptic, The Faceless
Brutal death metal: Suffocation, Aborted, Dying Fetus
Melodic death metal: In Flames, Dark Tranquillity, At the Gates
Deathgrind: Pig Destroyer, Misery Index, Cattle Decapitation
Death/doom: My Dying Bride, Paradies Lost, Anathema (early)
Deathcore: Bring Me the Horizon, Job for a Cowboy, Suicide Silence
Death metal is the most awesome genre ever. Too bad that everyone else besides 2 other people are scenes who listen to metal/deathcore and would probably melt under the intensity of death metal. I say "GORE NOT CORE" to them.