Acid rock got its name because it served as "background" music for acid trips in underground parties in the 1960s (e.g. the Merry Pranksters' "Acid Tests"). ("Acid" is a slang term for LSD.) In an interview with Rolling Stone Jerry Garcia quoted Grateful Dead band member Phil Lesh stating, "acid rock is what you listen to when you are high on acid." Garcia further stated there is no real psychedelic rock and that it is Indian classical music and some Tibetan music that are examples of music "designed to expand consciousness."The term "acid rock" is generally equivalent to psychedelic rock. Rolling Stone magazine includes early Pink Floyd as "acid-rock". In June 1967 wrote "From and transistors across the nation pulses the turned-on sound of acid-rock groups: the Jefferson Airplane, The Doors, Moby Grape". In 1968 Life magazine referred to as the "Kings of Acid Rock".
The term was much used in its heyday of the late 1960s and early 1970s, but has fallen into disuse; it is now only used as a means of putting this music into historical perspective.
When hard rock and heavy metal became prominent in the early and mid 1970s, the phrase "acid rock" was sometimes generically and erroneously applied to these genres. Over time, the common use of the term "heavy metal" replaced "acid rock" for these styles of music. Examples of hard rock bands once commonly called "acid rock" are: Alice Cooper, Vanilla Fudge, and Deep Purple.