Metal is a genre of rock music that developed in the late 1960s and early 1970s, largely in the United Kingdom and the United States. With roots in blues rock and psychedelic rock, the bands that created heavy metal developed a thick, massive sound, characterized by highly amplified distortion, extended guitar solos, emphatic beats, and overall loudness. Heavy metal lyrics and performance styles are generally associated with masculinity and machismo. The first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, though they were often critically reviled, 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; Mot?rhead introduced a punk rock sensibility and an increasing emphasis on speed. Bands in the New Wave of British Heavy Metal such as Iron Maiden followed in a similar vein. Before the end of the decade, heavy metal had attracted a worldwide following of fans known as "metalheads" or "headbangers".

In the 1980s, glam metal became a major commercial force with groups like M?tley Cr?e and Poison. Underground scenes produced an array of more extreme, aggressive styles: thrash metal broke into the mainstream with bands such as Metallica, Megadeth, Slayer, and Anthrax, 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 grunge and hip hop; and metalcore, which blends extreme metal with hardcore punk, have further expanded the definition of the genre.

Heavy metal is traditionally characterized by loud distorted guitars, emphatic rhythms, dense bass-and-drum sound, and vigorous vocals. Metal subgenres variously emphasize, alter, or omit one or more of these attributes. New York Times critic Jon Pareles writes, "In the taxonomy of popular music, heavy metal is a major subspecies of hard-rockthe breed with less syncopation, less blues, more showmanship and more brute force." The typical band lineup includes a drummer, a bassist, a rhythm guitarist, a lead guitarist, and a singer, who may or may not be an instrumentalist. Keyboard instruments are sometimes used to enhance the fullness of the sound. The electric guitar and the sonic power that it projects through amplification has historically been the key element in heavy metal. The lead role of the guitar in heavy metal often collides with the traditional "frontman" or bandleader role of the vocalist, creating a musical tension as the two "contend for dominance" in a spirit of "affectionate rivalry". Heavy metal "demands the subordination of the voice" to the overall sound of the band. Reflecting metal's roots in the 1960s counterculture, an "explicit display of emotion" is required from the vocals as a sign of authenticity. Critic Simon Frith claims that the metal singer's "tone of voice" is more important than the lyrics. Metal vocals vary widely in style, from the multioctave, theatrical approach of Judas Priest's Rob Halford and Iron Maiden's Bruce Dickinson, to the gruff style of Mot?rhead's Lemmy and Metallica's James Hetfield, to the growling of many death metal performers, and to the harsh screams of black metal.