Music is (rhythmically, melodically, and harmoniously) structured sound and silence.
What’s considered “music” and what’s considered “noise” is always culturally defined.
“Noise” is simply an unappreciated sound. Any sound could be “music” – to someone; but music is more than just sounds heard; it is also what is not. The space(s) between the notes, the paused silence between sounds, is what makes music more than noise.
All music has structure – almost always with sounds and rhythms that repeat. There are predictable build ups and releases of sound/energy. Every song has a beginning, a middle, and an end – and often a (vocal or instrumental) chorus and/or solo section.
There are many different kinds of music; and each is capable of creating some kind of physical and/or emotional response in the listener(s). Every sound is a form of energy at a specific vibrational frequency – and music can affect humans, animals, and even plants in many ways. Music often has the power to move us both physically and/or emotionally – causing us to sing, dance, laugh, cry, remember, reflect, think, or feel one way or another. Music can also anchor and evoke both memories of the past and aspirations for the future – in addition to influencing our responses in the present.
Major factors affecting the composition, instrumentation, and arrangement of music include where, when, and how, and by who it will be heard (and by who performed).
The physical environment (particularly the size, shape, and acoustics of anticipated venues and/or format in which it will be performed live or recorded and transmitted) is of far greater influence than many people may be aware. Music meant to be heard by one person is not the same as music meant to be heard by millions. Music meant to be played outdoors in a natural environment is different from music expected to be played in a stadium (requiring amplification), let alone what is suitable for a theater, opera house, night club, quiet restaurant, small piano bar, loud country bar, cramped hotel elevator, private automobile, doctor’s office, public building, or cellular ring tone, or (telephone) background music while waiting (“on hold”). (Pre-)Recorded and remixed music allows for options not available for music performed live in person – as does whether the music is intended to be listened to passively or to evoke some participation like singing, dancing, or some other active response to what is heard.
The social environment for which different music is intended includes the general culture/society as well as the ages, genders, status, and number of listeners and their anticipated or desired emotional state. Music for children or acceptable to all ages is not the same as what’s intended for adults drinking alcohol or for couples to dance to.