A peculiar circumstance attracted his attention: there seemed to be some kind of festivity going on, there were crowds of gaily dressed townspeople, peasant women, their husbands, and riff-raff of all sorts, all singing and all more or less drunk.
There are no more uses of "riff" in the book.
Show samples from other sources
The term, riff, was popularized by a Charlie Parker song.
And when the piano riff at the start of the New Pornographers’ "Challengers" kicks in, I know I’ve put myself in good hands.