A riff is a short piece of speech or writing that develops a particular theme or idea. Rowe does a very clever riff on the nature of prejudice. a repeated series of notes in popular or jazz music (Probably from REFRAIN)
A short melodic phrase that may be repeated and played as a solo or used as an accompaniment See Licks
A short musical phrase in jazz or blues It may be repeated often during a piece, with changes to the key, rhythm or melody, such as in Glenn Miller's swing hit In the Mood