The phenomenon which began in the 50's with the combination of rhythm and blues, country music, and gospel. It was pioneered by Chuck Berry, transformed by The Beatles, hardened by Led Zeppelin and AC/DC, and through the course of the 70's evolved into the pinnacle of musical glory.
Since then, it has lost the "Roll" and degenerated into "Rock" a generic term for all manners of crappy, modern, guitar driven music that has nothing to do with the messages, anthems, and ideals of old. Rather than professing a belief in the "Livin' easy, livin' free" lifestyle professed by AC/DC and their contemporaries, "Rock" now aims to piss and moan as much as possible whilst backed by horrible, rehashed guitar and pre-pubescent vocals about slutty girlfriends and cannabus.
AC/DC and Led Zeppelin are both gods in the pantheon of Rock 'n' Roll