riff 
(rĭf)
(rĭf)n.
1. Music A short rhythmic phrase, especially one that is repeated in improvisation.
2. A repeated or varied theme, idea, or phrase: gave us another of his riffs on the decline of civilization.
intr.v. riffed, riff·ing, riffs
To play or make riffs. Often used with on.
[Origin unknown.]