Almost everything they've done has been either Progressive or Psychedelic rock. There's no other way to define it.
Psychedelic yes. Progressive not so much. Atom Heart Mother is
very proggy, and Echoes is very self indulgent (IMHO, my mother completely disagrees with me on that), but over all I'd describe them as a Psychedelic Funk Blues Rock group who went through a proggy period between when Syd Barrett left and when the bells stop ringing on Time, with a surprisingly large Punk / New Wave influence in some of their later stuff.
I don't personally find them much more Proggy than Magazine or The Cure, who everyone says were Post Punk / New Wave groups. Pink Floyd were part of the whole Prog Rock movement, but when I think of Prog Rock I think of ELP playing like they've been possessed rather than Pink Floyd, a group of fairly talented musicans, who happen to be awesome songwriters playing songs, that happen to be awesome.
It's all opinion though, someone could come along and call The Sex Pistols prog rock, no one can say they're actually wrong, even though everyone else in the world will disagree with them. You can't prove anything (outside of mathematics anyway, and mathematics is just a construct created by humankind, and a surprisingly flexible one at that eg. 2+2=4, 2+2=10, 2+2=11. All correct, it just depends on the base of your counting system), especially something as vague as musical genre.
