I came across google's new book search, and entered in "prog rock." I came across a book called "Punk Productions: Unfinished Business." I clicked on it, and got to read a page from the book that contained my search of "prog rock." This is what I found:
"In terms of English bands, Led Zeppelin and Pink Floyd typify prog rock, while in the United States the Grateful Dead, the Allman Brothers, and Yes exemplify the sub-genre, as do Can and Hawkind in Germany. Prog rock bands tend to incorporate more musicians and instruments than previous rock bands did, including keyboards and a variety of wind and precussion instruments, while songs include lenghty solos, often for several of the band's musicians, and last for significantly longer than rock or pop songs. In 2004, prog rock continues but has been renamed "jam rock" and includes Phish, Blues Traveler, and bands that emerged from the Grateful Dead after Jerry Garcia died."
Well damn, this site needs to be renamed Jam Rock Archives! 