Heavy metal genres in the context of "Extreme metal"

Extreme metal is a loosely defined umbrella term for a number of related heavy metal music subgenres that have developed since the early 1980s. It has been defined as a "cluster of metal subgenres characterized by sonic, verbal, and visual transgression", and refers to metal that is harsher, heavier, more aggressive and less commercialized than other subgenres. Extreme metal is generally underground music that values authenticity and strives to remain outside the mainstream. The term usually includes thrash metal, death metal, black metal and doom metal. Some definitions do not recognise doom metal, or consider that only some of its subgenres are extreme. Most extreme metal styles have very fast tempos and originally took inspiration from hardcore punk.