This question is only interesting at the edge cases. We can all agree that "Mozart's Requiem" is music, and that the sound of me typing this answer isn't. In between there's a whole grey area that academics love to haggle over. If you fall in with the John Cage school of thought, any sounds that happen between specified points in time are music, just by you declaring them to be so. This is the basis of Cage's 4:33 -- the "music" is whatever sounds the audience makes during the "piece." I personally think the Cage definition is a bunch of baloney, and that the requirements should be stricter. I define music as sounds that are organized and patterned in time in order to convey or evoke emotion. What one person experiences as music, another may well experience as noise; see: Ethan Hein's answer to What distinguishes music from noise?
Written 23 Oct 2011