Black metal is an extreme subgenre of heavy metal. It often uses fast tempos, shrieked vocals, highly distorted guitars played with tremolo picking, blast beat drumming, and unconventional song structure. During the 1980s, certain thrash metal bands formed a prototype for black metal. This so-called "first wave" included bands such as Venom, Bathory, Hellhammer and Celtic Frost. A "second wave" arose in the early 1990s, mostly of Norwegian bands such as Mayhem, Burzum, Darkthrone, Immortal and Emperor. This scene developed the black metal style into a distinct genre.
Death metal is an extreme subgenre of heavy metal. It typically employs heavily distorted guitars, tremolo picking, deep growling vocals, blast beat drumming, minor keys, and complex song structures with multiple tempo changes.Building from the musical structure of thrash metal and early black metal, death metal emerged during the mid 1980s.
Doom metal is an extreme form of heavy metal music that typically uses slower tempos, low-tuned guitars and a much 'thicker' or 'heavier' sound than other metal genres. Both the music and the lyrics intend to evoke a sense of despair, dread, and impending doom. The genre is strongly influenced by the early work of Black Sabbath,who formed a prototype for doom metal with songs such as "Black Sabbath" and "Into the Void". During the first half of the 1980s, a number of bands from England (Pagan Altar, Witchfinder General), the United States (Pentagram, Saint Vitus, Trouble) and Sweden (Candlemass) defined doom metal as a distinct genre.
Power metal is a style of heavy metal music combining characteristics of traditional metal with speed metal, often within symphonic context. The term refers to two different but related styles: the first pioneered and largely practiced in North America with a harder sound similar to speed metal, and a later more widespread and popular style based in Europe (especially Germany, Italy, Scandinavia), Brazil and Japan (early Visual Kei bands) with a lighter, more melodic sound and frequent use of keyboards.
Sludge metal, or just sludge, is a subgenre of heavy metal that melds elements of doom metal, hardcore punk (or some other form of punk, such as crust punk), and sometimes Southern rock. Sludge metal is typically abrasive; often featuring shouted vocals, heavily distorted instruments and sharply contrasting tempos. While the style was anticipated by the Melvins from Washington, many of its earliest pioneers were from the state of Louisiana
Speed metal is a sub-genre of heavy metal music that originated in the early 1980s from NWOBHM and hardcore punk roots. It is described as "extremely fast, abrasive, and technically demanding" music. Speed metal eventually evolved into thrash metal.Although many tend to equate the two subgenres, there is a distinct difference between them. In his book Sound of the Beast: The Complete Headbanging History of Heavy Metal, Ian Christe states that "...thrash metal relies more on long, wrenching rhythmic breaks, while speed metal... is a cleaner and more musically intricate subcategory, still loyal to the dueling melodies of classic metal."
Thrash metal is an extreme subgenre of heavy metal that is characterized by its fast tempo and aggression. Thrash metal songs typically use fast, percussive and low-register guitar riffs, overlaid with shredding-style lead work. Thrash metal lyrics often deal with social issues using direct and denunciatory language, an approach which partially overlaps with the hardcore genre. The "Big Four" bands of thrash metal are Anthrax, Megadeth, Metallica and Slayer, who simultaneously created and popularized the genre in the early 1980s. The origins of thrash metal are generally traced to the late 1970s and early 1980s, when a number of bands began incorporating the sound of the New Wave of British Heavy Metal, creating a new genre and developing into a separate movement from punk rock and hardcore. This genre is more aggressive compared to its relative, speed metal, and can be seen in part to be a reaction to the lighter, more widely acceptable sounds and themes of glam metal.
So there you have it, METAL can mean any of the sub-genres. Every sub-genre is a "fusion" genre. Heavy Metal is the only "pure" genre.