a bellows is something that blows air into a small opening in order to make something work. the bellows will have a kind of sack which has air in it. when the sack is squeezed the air is pushed out. bellows can be quite small and operated by hand, for example for stoking a fire in an open fireplace. they can also be very large, such as bellows that produce air for a large pipe organ to be played. such bellows used to be pumped by hand (sometimes by several people), but nowadays electricity is used. bellows are used by blacksmiths or metalworkers for smelting and welding. they are also used in small musical instruments such as bagpipes, accordions and concertinas. the harmonium has bellows which the player operates by pumping with the his feet.