Def Leppard are an English hard rock band from Sheffield who formed in 1977 as part of the New Wave of British Heavy Metal. On the strength of their albums, Pyromania and Hysteria, Def Leppard became one of the top selling rock bands of the 1980s.

The music of Def Leppard is a mixture of hard rock, AOR, and heavy metal elements, and has been associated more with the glam metal movement of the 1980s than with the NWOBHM of the late 1970s, in large part due to their mainstream success and production. However, Def Leppard have expressed dislike of the "pop metal" label.

By the release of the Hysteria album, the band had developed a distinctive sound featuring heavily processed drums and effects-laden guitar sounds, overlaid with a multi-layered wall of husky, harmonised vocals. Def Leppard is one of only six rock bands with two original albums selling over 10 million copies each in the U.S. The others are The Beatles, Led Zeppelin, Pink Floyd, Eagles and Van Halen.