A music genre is a conventional category that identifies pieces of music as belonging to a shared tradition or set of conventions. It is to be distinguished from "musical form" and "musical style", although in practice these terms are sometimes used interchangeably. There are numerous genres in Western classical music and popular music, as well as musical theatre and the music of non-Western cultures. The term is now perhaps over-used to describe relatively small differences in musical style in modern rock music, that also may reflect sociological differences in their audiences. Timothy Laurie suggests that in the context of rock and pop music studies, the "appeal of genre criticism is that it makes narratives out of musical worlds that often seem to lack them".