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." The term usually refers to a more abrasive, harsher, underground, non-commercialized style or sound associated with the doom metal, speed metal, thrash metal, black metal, and death metal genres. Extreme metal exists in a relationship with hardcore punk, which was a founding influence on all of its main genres except doom metal and has fused with it in the forms of crossover thrash, crust punk, grindcore, sludge metal and metalcore. Though many extreme sub-styles are not very well known to mainstream music fans, extreme metal has influence