Fish Smell level, in the vaginal sense of the word fish.
Man, you'd never believe the FSL on that ho.
Short for 'Fantasy Slut League' - similar to a Fantasy Football League except you draft real people and are awarded points for 'documented' sexual encounters with them. Frequently organized by high school males without informing the female draftees.
League Member: I had a three-way with two of my draft picks this weekend. *shows phone pic*
League Commissioner: Encounter is validated and I award you +24 points, making you the FSL points leader.