I. riff¹ /rɪf/ noun [countable]
[Date: 1900-2000; Origin: Probably from ⇒ refrain²]

1. a repeated series of notes in popular or jazz music:
a guitar riff

2. a piece of speech in which someone talks about a subject in an entertaining way that does not seem planned:
He goes off on a riff about the problems of being middle-aged.

[TahlilGaran] Dictionary of Contemporary English ▲

II. riff² verb [intransitive]

1. to play different notes related to the main tune in popular or jazz music:
He was riffing on his guitar.

2. to talk about a subject in an entertaining way that does not seem planned:
During her show, she riffs about everything from her family to global warming.

[TahlilGaran] Dictionary of Contemporary English ▲