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Apart from the five major genres of heavy metal (thrash, death, black, power and doom),
there are many other sub-genres in existence:

  Alternative metal is a cross-genre term used to describe heavy metal bands with a pronounced experimental edge. Bands often use typical heavy metal instruments, but include unconventional lyrics, odd time signatures and unusual technique. In many instances it is described as a fusion of metal and alternative rock. Prominent bands in this genre include Tool and System Of A Down.  
  Avant-garde metal (sometimes called experimental metal) is a cross-genre term used to describe metal bands that exhibit experimentation through non-standard sounds, instruments and song structures akin to the genre of metal they are rooted in. Prominent examples include Arcturus and Celtic Frost.  
  Cello metal is characterised by the use of cellos, as well as other bowed string instruments such as the violin and viola, as primary instruments, alongside or in place of more traditional rock instruments such as electric guitars, electric bass guitar and drum set.  
  Christian metal is a cross-genre term used to describe metal bands that introduce Christian themes into their lyrics. This sub-genre has a long tradition within metal, starting with Christian hard rock bands springing up alongside the NWOBHM phenomenon to the Christian metalcore bands today. Often the Christian themes are melded with the subjects of the genre the band is rooted in, generally providing a Christian take on the subject matter. Examples include Stryper, Tourniquet, P.O.D. and Mortification.  
  Crust punk (often simply crust) is one of the evolutions of anarcho-punk and hardcore punk, mixed with extreme metal guitar riffs. The style, which evolved in the mid-1980's in the UK, often had songs with dark, pessimistic lyrics, lingering on political and social ills. It is typically played at a fast tempo with growled and screamed vocals and anarchist lyrics. Notable crust punk bands include Amebix, Antisect and Doom.  
  Extreme metal is a cross-genre term used to describe heavy metal that is considerably heavier, faster, more aggressive and more abrasive. For example, vocalists may often use death growls or high-pitched shrieks and more obscene lyrics, drummers may often use blast beats, and the band's appearance may be intended to shock. Bands of this grouping are typically of the black metal, death metal, doom metal and thrash metal genres. The term is also used when a band is musically "extreme" enough but does not conform easily to any of the extreme metal genres. Bands of this calibre include Cradle Of Filth, Celtic Frost and Strapping Young Lad.  
  Folk metal developed in Europe during the 1990's. As the name suggests, the genre is a fusion of heavy metal with folk music. This includes the widespread use of folk instruments and, to a lesser extent, traditional singing styles. Examples in this genre include Skyclad, Finntroll, Heidevolk, Korpiklaani, Ensiferum, Turisas and Moonsorrow.  
  Funk metal is essentially a fusion of heavy metal and funk. It start of in the late 1980's as a sub-genre of alternative metal, and was heavily influenced by alternative rock bands such as Red Hot Chili Peppers and Fishbone. Funk metal was also one of the key influences of the nu metal genre. Notable funk metal bands include Primus, Living Colour, Faith No More and Rage Against The Machine.  
  Glam metal (also known as hair metal) is a term used to describe the visual style of certain heavy metal bands that arose in the late 1970's and early 1980's in the United States, particularly on the Los Angeles Sunset Strip music scene. It was popular throughout the 1980's and briefly in the early 1990's, combining the flamboyant look of glam rock and playing a commercial hard rock/heavy metal musical style. "Hair bands" was the term popularised by MTV in the 1990's and derives from the tendency among glam metal acts to style their long hair in a teased-up fashion. Many of the bands donned make-up to achieve an androgynous look, similar to that of some 1970's glam rock acts. Motley Crue, Poison and Twisted Sister are examples of bands who adopted the glam metal look in their stage attire and their music video imagery.  
  Gothic metal is characterised as a combination of the dark melancholy of gothic rock with the aggression and sonic power of highly amplified heavy metal music. The genre originated during the mid-1990's in Europe as an outgrowth of doom/death, a fusion genre of doom metal and death metal. Examples of gothic metal bands include Paradise Lost, Lacuna Coil, Type O Negative, Moonspell, My Dying Bride, Elis, Sirenia, Stravaganzza, Theatre Of Tragedy and Tristania.  
  Grindcore is a fusion of crust punk and thrash or death metal. It is characterised by growling vocals, blast beats, and incredibly short songs with lyrics that are often focused on gore and violence, though sometimes the lyrics can be political. Grindcore, in contrast to death metal, is often very chaotic, and lacks the standard use of time signatures. The style was pioneered by the British band Napalm Death in the 1980's. Other notable grindcore bands include Carcass, Brutal Truth and Pig Destroyer.  
  Groove metal (also known as neo-thrash, post-thrash or power-groove) consists of slow or mid-tempo and down tuned thrash riffs, bluesy guitar solos, greatly emphasised drum work and harsh vocals. Examples of groove metal include Lamb Of God, Pantera, Machine Head, Fear Factory and Sepultura.  
  Industrial metal combines elements of industrial music and heavy metal. It is usually centred around repetitive metal guitar riffs, sampling, synthesizer or sequencer lines, and distorted vocals. Prominent industrial metal groups include Ministry, Nine Inch Nails, Marilyn Manson and Godflesh.  
  Metalcore combines elements of hardcore punk with one or more of heavy metal, thrash metal and extreme metal. Generally, metalcore guitarists use harmonised guitar riffs and solos, drummers use hardcore d-beats and double bass drums, and vocalists use a sing-along style. A distinguishing characteristic is the "breakdown", whereby the song is slowed to half-time and the guitarists play open strings to achieve the lowest-pitched sound. Metalcore generally differs from thrash metal in that it avoids the "chugging" guitar sound and focuses more on melody than aggression. Prominent metalcore bands include Bullet For My Valentine, As I Lay Dying, Killswitch Engage, All That Remains and Shadows Fall. In the early 1990's, a third wave of metalcore groups appeared, who placed significantly greater emphasis on melody. These bands tend to fuse melodic death metal, hardcore punk and sometimes emo. Melodic metalcore bands include Atreyu, Avenged Sevenfold, Darkest Hour, Eighteen Visions and Poison The Well. These groups took major influence, cues, and writing styles from Swedish melodic death metal bands, particularly At The Gates, Arch Enemy, In Flames and Soilwork. Melodic metalcore frequently makes use of clean vocals.  
  Neo-classical metal, also known as shred metal, is a sub-genre that is heavily influenced by classical music in its style of composition. It uses a very technical style of guitar soloing called shred guitar, in which guitarists use cross-picking, sweep picking and economy picking to play rapid scales and arpeggios. As well, it uses elements borrowed from classical music, including instruments, scales and melodies. Yngwie J Malmsteen, Tony MacAlpine and Vinnie Moore are prominent performers in this genre.  
  Nu metal is a fusion genre that blends heavy metal elements with other styles, including grunge and hip hop. The style is mostly syncopated and based on riffs, and is influenced by groove metal rhythm. Some nu metal bands use seven-string guitars, which are sometimes down tuned to increase heaviness, resulting in bass guitarists using five and six-string instruments. Turntables, sequencers and samplers are sometimes included. Nu metal vocal styles range between melodic singing, rapping, screaming and death growling. In 1994, Korn became the first band labelled as nu metal. Slipknot, Linkin Park, Deftones and Korn are prominent bands in this genre.  
  This heavy metal movement takes influence from post-rock. While it is in many ways similar to post-rock, post-metal tends to include lower-tuned guitars, distorted guitars, heavy atmospherics, gradual evolution of song structure, and a minimal emphasis on vocals. Post-metal stresses emotion, contrasting the ambiance of post-rock with the weight and bombast of metal. Vocals are de-emphasised or non-existent, and lyrics tend to be equally abstract, often thematic or philosophical in nature. It is largely an American phenomenon, but also includes some Japanese bands. Bands like Neurosis, Isis, Cult Of Luna and Pelican write lengthy songs (typically five or six per album) that can range from light and guitar-driven  to heavy, drum and bass-driven.  
  Progressive metal is a fusion between progressive rock and heavy metal. It is one of heavy metal's more complex genres, due to its use of of unusual and dynamic time signatures, long compositions, complex compositional structures, and skilled instrumental playing, where instrumental solos are detailed and extended. However, the latest age of progressive metal has favoured rougher lyrics and lower-pitched riff sequences with high amounts of strumming. Vocals, if present, are melodic (though there are a few that utilise unclean vocals), and lyrics are often philosophical, spiritual or political. Many bands of the genre were influenced by the progressive rock band Rush, who would often incorporate elements of heavy metal into their music. Examples of the genre include Queensryche, Dream Theater, Opeth and Tool.  
  Rap metal is a cross-genre term used to describe bands that institute the vocal and lyrical form of hip hop. Examples of rap metal include Limp Bizkit, Stuck Mojo and Rage Against The Machine. Often mis-labelled as nu metal, which has similar elements in the music, rap metal usually does not include turntables or sampling into its sound, although keyboards are often used.  
  Speed metal originated in the late 1970's and early 1980's and was the direct musical progenitor of thrash metal. When speed metal first emerged as a genre, it increased the tempos that had been used by early heavy metal bands, while retaining their melodic approaches. Examples of speed metal include Venom, Motorhead, Annihilator and Accept.  
  Stoner metal is typically slow-to-mid tempo, low-tuned and bass-heavy. It combines elements of psychedelic rock, blues-rock and doom metal, often with melodic vocals and "retro" production. The genre emerged during the early 1990's and was pioneered foremost by the Californian bands Kyuss and Sleep. Other prominent stoner metal bands include Acid King, Electric Wizard and Sons Of Otis.  
  Symphonic metal varies in form. It most commonly refers to heavy metal bands that use orchestral elements in their music. These elements include full orchestras, opera themes, vocals or keyboard playing akin to that of opera or symphony music, and a softer and a more upbeat nature than other metal genres. Prominent examples include Nightwish, Within Temptation, Epica and Therion.  
  Traditional heavy metal, also known as classic metal, or often simply heavy metal, is a recent umbrella term describing bands and artists who play a metal music style similar to the style heard before the genre evolved and splintered into many different styles and sub-genres. It is characterised by mid-to-fast tempo riffs, by thumping basslines, crunchy riffs, extended lead guitar solos and clean, often high-pitched vocals and anthemic choruses. It is not generally categorised as a sub-genre of metal, but the main genre of it. Examples include Deep Purple, Black Sabbath, Blue Oyster Cult, Alice Cooper, Judas Priest and Iron Maiden.