1. A reed used with certain woodwind instruments, such as the bassoon and the oboe. The double reed is actually two pieces of reed, formed into thin blades at the tip and into a tube at the bottom end, which is attached to the instrument.

Instruments that use double reeds have no other mouthpiece -- the reed acts as the mouthpiece. To play most modern double reeds, the tip of the double reed is inserted partway into the mouth, with only the lips touching it. The lips are drawn firmly around the reed. My bassoon teacher suggested students use the image of a drawstring bag when forming their embouchure. Sound is produced when the blades of the reed vibrate.

2. Also, a term referring to the class of instruments that use double reeds. The standard double reeds of the modern orchestra include the oboe, the english horn, the bassoon, and the contrabassoon.

Bagpipes are also a double reed instrument, having a double reed in each chanter and drone. With bagpipes, these reeds aren't placed in the mouth, but are enclosed in a tube, and vibrate as air from the bag is forced through them.

The shawm is a double reed instrument, similar to an oboe but without keys, that was used in medieval and renaissance times. It arose in Arabic regions and made its way to Europe during the Crusdades.

Another traditional double reed is the crumhorm, which is a curved wooden tube with a cylindrical bore, and a reed which is covered by a wooden cap with a slit at the top that the player blows through.

The rackett, or "sausage bassoon" is another Renaissance double reed which consists of a block of wood or ivory around a foot in length and several inches thick, which has multiple (often around 9) parallel bores drilled through it, each connected with another bore at each end. This has the result that the bore of the instrument snakes through the block of wood, having an actual length that is nine times the length of the instrument, so you can get a surprisingly low note out of a small instrument.