Originally Posted by
Mirage
I would say rap isn't just poetry, it's a technique. It's in what way you speak, and to a certain extent how you rhyme and stuff. This can be done both with and without a rhythm, but it would in most cases be easier do to it with one, I'd say.
The music that most rapping is done to to is what I think of as hip hop. This music can also be made without lyrics, for example RJD2 and DJ Shadow make hip hop and hip hop influenced music with few or no lyrics.
I think these two terms are sometimes not distinguished between because in almost all cases, rapping is done to hip hop music. I have however heard people rap to both techno, rock and metal too :p.