There isn't one answer. A definition is ultimately a consensus of perception. Useful for a lot of things, but not necessarily the whole picture.
Ok, here's my "definition" of music:
Like they say, everything's everthing, and everything vibrates at some level. So "Music" is whatever part of that everything that you can want/need it to be. If it's your foot, hey, cool. That certainly falls outside of any consensus that I know of, but that doesn't mean that if you tell me that your foot is music and I can't hear/feel it that it's not. It just means that I can't want/need it to be. And that may or may not be my loss. Probably not, but you never know...