Sound. What is sound? And what about rhythm, melody, harmony? And vibration, and noise?
Welcome to the wonderful world of acoustics, where all these concepts come into play to give us ways to study and appreciate this Universe of ours, where "everything vibrates". And that includes us human beings ...
Here is one of the best starting points on the subject of sound: Acoustics.org, a service of the The Acoustical Society of America.