The term
progressive rock
is most commonly used in reference to the art-rock movement of the 1970s. The movement joined rock instrumentation with a classically influenced approach to compositional and harmonic structure. In the larger sense, the term can be applied to the journey that rock'n'roll made from being a purely commercial form of popular music to becoming a serious artistic endeavour. This journey was made more or less simultaneously in the U.K. and the U.S...