Felix did get the definition right, it was a radio label for what was known in the late 60's and 70's as AOR, and is typically what we think of today as harder rock, rather than rock and roll in the early Chuck Berry or Elvis sense. It's starting point may actually be what the Stones and Beatles did with the stuff from the Chess catalog, and morphed through psychedelia (Hendrix and Cream) and Brit blues driven rock (Cream and Led Zep) into a variety of directions, some of it country influenced (Eagles), some of it what we now think of as 'progressive' (YES, ELP), but in my mind stops with grunge, which is Nirvana. In the middle, you have some pretty heavy rock stuff, like Black Sabbath, some operatic hard rock (like Queen), bands like Aerosmith and AC/DC, which you could either say were guitar driven or derivative of the whole Zep thing with the wailing lead singer. Mostly guy stuff, although Janis fits. I'm probably still not capturing it, but I know it when I see it- it's what the guys in Pittsburgh where I grew up would find acceptable to listen to and not think you were a wimp (or worse).
