“Whah yew puttin’ them strange ad-ject-tives in fronta ‘rock’, thar, boy?”
Well, suffice it to say that progressive rock (“prog rock” to insiders) just ain’t the same as your three-chord “I Wanna Hold Your [choose appendage based on decade and local obscenity laws]” bop-till-you-drop stuff.
But that doesn’t mean it’s easy to define. Ontological discussions (read: flame wars) of what is or isn’t prog rock abound in the appropriate circles amongst those with waaay too much time on their hands.
However, you can say a few things about it. It’s generally a reaction against the overly simple, one-theme pop music of the day (which usually revolves around the placement of various people’s body parts in some relationship to other people’s body parts as the key to happiness or the lack thereof–which is strange, since the body parts themselves aren’t usually the ones with psychological problems). It usually has some complexity involved, in some aspect of the music. That’s about as common as it gets.
Apart from that, anything goes. Still, most people agree that certain things *are* prog, and argue about the rest. Some people claim that the Beach Boys, the Beatles, or even Michael Jackson are prog (though the last one may refer more to lifestyle than music). But generally there are a number of bands which continually are discussed under the rubric of prog rock and you begin to have a feel for what is prog and what isn’t. Note that this feel is usually based on your own tastes and is quite different from other people’s–you’ve probably adopted one of the many subgenera of the, uh, well, genre.
Did I say “subgenera”? (Actually, I just wrote it.) Yes, prog has developed tons of subgenera to fill the heart of the most anally-retentive catalogue librarian on the planet. There’s Classic Prog, Classical Rock, Symphonic Rock, Canterbury, Neoprog, Progressive Metal, “Prog-influenced”, Italian prog, German prog (or “Krautrock”), French prog, Spanish prog, psych, space music, neo-psych, and…you get the picture. The bands everybody’s heard are: King Crimson; Emerson, Lake & Palmer; Genesis; and Yes. Also-rans are Rush and Pink Floyd, though classification wars usually erupt at their mention.
“So you’re not actually going to tell me what it is, or anything.”
Righty-ho, reader-boy! I can’t. When I’m less lazy I’ll include links to a couple of other people’s attempts at defining what prog is, but the ultimate answer is “go and listen to a few of the bands that self-described prog fans listen to and figure it out for yourself.” Fortunately, the Web is a great place for that, and you can try before you buy. Get the higher-rate audio samples, though, because this kind of music really benefits from it. Then you will think you know what it is and will get in a few flame wars about it in no time. Enjoy!