Science doesn't have a definition, according to the author of Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School.
Well, here's mine.
Music is a non-spatial pattern made by sound and completed over time, for the purpose of creating an atmosphere or evoking an emotional response.
Thus, music is always subjective, since it always aims for an emotional response -- even if it's a cool one -- in the listener, and how we listen depends on our own musical faculties, emotional disposition, intellectual grasp, and hearing. Music is a pattern, like wallpaper shapes are a pattern, but though a wallpaper pattern can be perceived within seconds, a musical pattern requires time, and in that way it is like the body, always moving forward in time. Dance and music, of course, are perfect partners, and we often feel moved to sing or tap our feet to music, to be a part of the pattern's completion in a bodily way. Because music is about patterns that can be highly intricate, subtle, and refined, music can be one of the most intellectually sophisticated of the arts; but because music also engages the body with its simple drive forward in time, it can be one of the most primitive, direct, and universally accessible arts.
Unlike some other arts, music can be simple without being low, while simple architecture tends to be low rather than high (a log cabin or a public lavatory, for instance). The simplicity of music can be as much a part of its beauty as complexity. In fact, I would argue that great music requires both simplicity and complexity in the pattern (or the piece, as we call it). It requires that which can immediately be recognized as the beginning of a drama, and it requires details to be discovered in subsequent listenings, even after the listener has learned 'the plot'.