Heavy metal is a classification of rock music that appeared in the late 1960's and early 1970's. It is characterized by loud or distorted guitars, emphatic rhythms, dense bass, drum sound, and aggressive vocals. It did not become prevailing until 1980 were when glam metal became popular. Groups such as Motley Cr, Poison, and Def Leppard were getting radio airplay.
In 1987, MTV launched a show, Headbangers Ball, which was devoted exclusively to heavy metal videos. Thrash metal also broke onto the scene with bands such as Metallica, Slayer, Megadeath, and Anthrax. Heavy metal fans became known as "metalheads" or "headbangers."