A large rounded piece of tissue paper that is designed to be placed over a toilet seat to protect the shitter from "germs" that may be residing there. The rounded section lies on top of the toilet seat (thus creating the essential Buttock-porcelain Barrier) while a cutout center flap hangs down into the toilet causing the entire paper to be sucked into the toilet when it is flushed. Seat protectors are typically contained in a dispenser on the wall of a public bathroom stall in such venues as airports and offices.
Note that the Buttock-Porcelain Barrier provided by the seat protector creates a false sense of security since someone else's bodily fluid on the toilet seat can leak right through the S.P.'s thin, porous surface. I doubt germs are foiled either.
Toilet User: Damn these seat protectors! I can't get one out of the dispenser without ripping it!
Toilet User: Ugh! Who keeps using 20 seat protectors at a time and clogging the handicap stall?