Heavy metal (often referred to simply as metal) is a genre of rock music that developed in the late 1960s and early 1970s. With roots in blues-rock and psychedelic rock, the bands that created heavy metal developed a thick, massive sound, characterized by highly amplified distortion and extended guitar solos. Allmusic states that “of all rock & roll’s myriad forms, heavy metal is the most extreme in terms of volume, machismo, and theatricality.”

Heavy metal has long had a worldwide following of fans known as “metalheads” or “headbangers”. Although early heavy metal bands such as Black Sabbath, Led Zeppelin, and Deep Purple attracted large audiences, they were often critically reviled at the time, a status common throughout the history of the genre. In the mid-1970s, Judas Priest helped spur the genre’s evolution by discarding much of its blues influence. Bands in the New Wave of British Heavy Metal such as Iron Maiden and Motörhead followed in a similar vein, introducing a punk rock sensibility and an increasing emphasis on speed.

In the mid-1980s, pop-infused glam metal became a major commercial force with groups like Mötley Crüe. Underground scenes produced an array of more extreme, aggressive styles: thrash metal broke into the mainstream with bands such as Metallica, while other styles like death metal and black metal remain subcultural phenomena. Since the mid-1990s, popular styles such as nu metal, which often incorporates elements of funk and hip hop; and metalcore, which blends extreme metal with hardcore punk, have further expanded the definition of the genre.