1. vulgar slang Of a woman, to masturbate. A play on the masculine version "jack off" and the nursery rhyme "Jack and Jill."
2. vulgar slang To stimulate a woman's genitals, especially to the point of orgasm, by means other than sexual intercourse or cunnilingus.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.