Riff (noun)

1. A repeating phrase or melody, especially in jazz or rock music.
2. A short, improvised solo passage in a piece of music.
3. A theme or subject that is recurrent or repetitive.

Origin:

Origin uncertain, probably from english dialectal riffle to rush along or from english dialectal riffe to move with quick jerky motions.

Examples:

1. The band played a catchy riff throughout the song.
2. The guitar player played a blues riff.
3. He came up with a new riff for the song.
4. The riff in the song was used as the main melody.
5. The story had a repeated riff of the main character's struggles.