The act of stacking two females on top of each other so their beavers, when aligned properly, form a seal similar to the gap between teeth, allowing just enough room for a penis to fit between them and perform a flossing action.
Brian: "So what'd you do this weekend?"
Cody: "I invited that new girl Sarah over to for dinner with Katie and me. One thing led to another and I ended up flossing the beavers."
Fraternal twins that are conceived between one mother and two different fathers, usually at an orgy or gangbang.
Skylar: Wait you guys think I'm dating Trayvon? Eww gross, we're half twins!