A flatulent-sounding explusion of air from the vagina, caused by the pumping of air into it with one's penis, or the spasming the vagina can go through during oral sex, "gulping" in and eventually expelling air.
When Stacey queefed while I was making love to her orally, it startled the hell out of me, we both laughed, and I dove right back in. I quickly learned that her queefs were her body's way of showing how much she loved what I was doing and I welcomed them.