Punk rock is an anti-establishment music movement that began about 1974-1975 (although precursors can be found several years earlier), exemplified by The Ramones, the Sex Pistols, The Voidoids, The Altar Boys, The Damned, and The Clash.

The term is also used to describe subsequent music scenes that share key characteristics with those first-generation "punks," and it is often applied loosely to mean any band with "attitude" or "youthful aggression." The term is sometimes also applied to the fashions or the irreverent "DIY" ("do it yourself") attitude associated with this musical movement.

Cited from Wikipedia.