Depends on what source you believe. Some say 'rock and roll' originally meant to have sex, originating in the ghetto. Others say Alan Freed coined it first on his radio show.

Waylon Jennings made this comment about country music, but I think it can also be applied to 'rock' as well...I like it :)

'Country music isn't a guitar, it isn't a banjo, it isn't a melody, it isn't a lyric. It's a feeling.'