Heavy metal (often referred to simply as 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, and emphatic beats. Allmusic states that "of all rock & roll's myriad forms, heavy metal is the most extreme in terms of volume, machismo, and theatricality."
Early 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; Motörhead 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."