I've seen more than one definition of music written to exclude a particular style. ACD likes to say that music that doesn't contain a cohesive narrative - read "music ACD can't follow" - is gibberish, and not music. His definition excludes...hmmm...whichever composers he says it excludes. He has specifically named Stockhausen, Cage, and Carter. I have seen a definition written to exclude rap.
Doesn't work for me. It's fine to dislike a style, any style; I support your right to hate any music you can't tolerate, can't follow, run away from. But it's intellectually dishonest to justify your dislike by claiming the composer or style is at fault: it's just not music!
I'll propose a definition of music broad enough to include all styles worldwide: Music is organized sound moving in time.
I'm modestly uncomfortable with that definition, but for a very specific reason: by "organized" I do not mean to exclude aleatoric music, where there are elements of chance or where the performer is asked to make something up on the spot. What I mean by "organized" is that the composer's mind has been brought to bear in organizing or making decisions or giving instructions about the work, not that any particular process of organization is expressed in the work.
I suppose the definition could be broadened a bit: Music is organized sound moving in time, usually, but not invariably, incorporating at least one of melody, harmony, and rhythm or meter.
