Sub-genre of rock
also known in short as "prog".
It relies as much on complex, painstakingly composed and arranged structures that rival classical music
(Gentle Giant, BMS, Yezda Urfa), as on improvisation that rivals jazz
(VDGG, Soft Machine, ELP). It may employ any device to boost its quality (unusual instruments, elements from other genres, non-standard structures), as it is a genre essentially associated with musical freedom. Prog pieces often extend beyond a 5 minute limit, though it is not always the case (Gentle Giant, Jethro Tull).
Its primordial purpose was to bring much-needed credibility to rock'n'roll
, while unifying the different realms of "good music" and exploiting its potential to the fullest. Sadly, it has drawn a large amount of snobbish minions in the process.
It thrived in the 70s, after which many of its most brilliant exponents, even Pink Floyd or ELP, not to mention Gentle Giant, just started getting it wrong. It was no longer progressive rock, but a kind of "tired uninspired unchallenging get-with-the-times-old-man sing-along" rock.
Additional Note: Male prog fans who believe this is not a genre enjoyed by those loosely referred to as "girls" need to be more "progressive" so as not to shame their kind. They are suggested to start by not making gratuitous generalizations, and realizing they're looking for female companionship in the wrong place.
P.S.: I'm not even a feminist
but that's just lame
Genesis is one of the many progressive rock groups that have tarnished their legacy by going top 40
A progressive rock fan should know better than to think like an emo kid
Me and my girls like progressive rock: we shake our booties to "21st Century Schizoid Man" and sway with the fellas to "Shine on You Crazy Diamond".