Music is a very subjective thing, and varies from one culture to the next. My following attempt to describe it is inherently going to be just one person's limited perspective.
In my experience, music has one or more of the following properties, in no particular order:
- Harmonies: several notes playing at once, or in quick succession, that suggest a chord.
- Rhythms: notes whose timings sound good and quite possibly make you want to dance. These may or may not be pitched.
- Melodies: the bits you hum in the shower. These usually reinforce the chords, or at least the keys.
- Timbres: the sounds the notes are played on. In electronic music, the sounds are important to the extent that the music needs to be simple so as not to distract from the sounds' dynamic variation. This is especially true of, for example, acid house.
- Words: a lyric elevates an otherwise instrumental piece of music into a fully fledged song, giving its emotions a context. A song is harder to create and easier to digest than instrumental music, in much the same way a film is harder to create and easier to digest than a novel.
Essentially, music is a set of carefully constructed patterns of sounds, balancing a fine line between being too repetitive or too chaotic. Much of the craft of making music is about finding a good balance.
These are all simply general guidelines. You're welcome to explore and test their limits. A drum solo is pure rhythm and timbres, with no harmonies, melodies, or words. No chords, keys, or pitches of any kind. It's still very much music. At the other extreme, ambient music tends to focus on simple, repetitive harmonies that showcase their sounds, often with little to no real rhythms, melodies, or words. There are no rules, only experiments. Try things out!