Pernouced four KD or FKD. A term used by straight dudes lesbians and anyone whos finger fucked a pussy, meaning four knuckles deep. This can be expanded to include any number of knuckles deep in a pussy.
Bobby: have u seen devins mom?! Shes a total MILF!
Jake: yeh i was totally FKD in herlast night.
Bobby: FR?