Here’s an extended quote from the audio course Understanding the Fundamentals of Music by Robert Greenberg, lecture 1.

Music is a language; a mode of sonic communication through which a tremendous amount of information of all sorts — aesthetic, stylistic, emotional and so forth– can be transferred with an ease that belies its complexity. […] I would suggest that music is the ultimate language — a mega language — a language in which our hard-wired proclivities to use successions of pitches and sounds to communicate are exaggerated, intensified, and codified into a sonic experience capable of infinitely more expressive depth and nuance than mere words alone. […] The great mid-century composer, Roger Sessions (who was the teacher of my teacher, a gentleman named Andrew Imbrie) said that music is the “controlled movement of sound in time”. Although we respectfully ask, “Controlled by whom?” Our working definition will draw on what is best from Sessions’ definition. Music is sound in time — or, if you prefer — time ordered by sound. That’s it! And that’s enough. That definition isolates the two essential aspects of music — sound and time — without any qualifications.