I was wondering precisely about fugues! they do feel like very complex variation and ornamentation of a motif, aren't they?

Then, some pieces are really centered around theme repetition, it feels. Ravel's Boléro. Pachelbel's canon. Carrol of the Bells. Looks like there's different names for that - canon, ostinato.

And then there's the use of motif and repetition/variation/ornamentation in improvisation, such as in jazz. I am not a music scholar so I can't explain how it works, but I know that they use it...

Maybe you can tell us more?