A game/activity usually played with friends at a bar type environment in which one person comes up with a random object and a place, and the other people involved have to create an inappropriate sexual act, described and titled by the object & place given.
Friend A: (place) Mississippi (object) Motorboat
Friend B: "O.K. a Mississippi Motorboat is when you're getting a blow job from someone with no teeth and as they're sucking on your dick you plug their nose to cause them to try and breath through there mouth, thus making their cheeks slap against your shaft, resembling the sound of a motorboat engine."
Alabama Turkey Baster was the first term coined, hence the name of the game.