Muff diving is a slang phrase to refer to cunnilingus or the act of performing oral sex on a woman. Muff, historically, refers to a piece of fur clothing. The slang phrase 'muff diving' pertains to a woman's pubic hair, which one needs to dive into in order to reach the clitoris, labia, and the rest of the vulva. Muff diving involves the direct stimulation of the clitoris, the most sexually sensitive part of a woman's body.