What is Progressive Rock?

Progressive Rock is an affectedly genteel style of rock music, dotted with elements of pomposity and grandeur. The whole Progressive Rock movement was believed to have emerged somewhere around the late 60's in England. It reached the pinnacle of its popularity during the 70's but there are vestiges of this movement even today.
Some of the common features of Progressive Rock are:
1. Concept albums - Pink Floyd's "The Wall", Yes "Close to the Edge", Rush "2112", early Genesis "The Lamb Lies Down on Broadway"
2. Tonnes of electronic and/or simulated sound systems - Pink Floyd, Rush, King Crimson
3. The need to borrow or redefine a classical piece of work - Emerson, Lake and Palmer's "Hoedown" inspired by Aaron Copland's Rodeo, Yes' "Siberian Khatru" inspired by Igor Stravinsky's "Rite of Spring" , Jethro Tull's "Bouree" cover of the original by JS Bach
4. Creating song structures similar to classical suites, i.e., dividing the song into movements - Yes' "Close to the Edge", ELP's "Tarkus", Rush's "Cygnus X/1"