The word siphon (from Ancient Greek: σίφων "pipe, tube", also called syphon) is used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in a narrower sense, the word refers particularly to a tube in an inverted 'U' shape, which causes a liquid to flow upward, above the surface of a reservoir, with no pump, but powered by the fall of the liquid as it flows down the tube under the pull of gravity, then discharging at a level lower than the surface of the reservoir it came from.