PTFE, which stands for polytetrafluoroethylene, is a synthetic fluoropolymer of tetrafluoroethylene, most commonly known as Teflon. Teflon tape is a very thin, white tape used to wrap around the threaded ends of pipes to improve the watertightness of a joint. Though PTFE tape is fairly common thing to use, not many people know how to actually use it properly, or where to use it. A lot use it on compression joints, but you really don't need to unless it leaks. You would use it on a radiator valve. Check out this video tutorial to learn how to use PTFE tape (Teflon tape) on threads for sealing pipes and fittings.