short flute having a stopped lower end and a flue that directs the player's breath from the mouth hole at the upper end against the edge of a hole cut in the whistle wall, causing the enclosed air to vibrate. Most forms have no finger holes and sound only one pitch. It was made originally from bird bones, and it is considered by many scholars to be the oldest flute type known. It is mainly used for signaling, though it can be heard in folk ensembles and in contemporary music.

If a pellet is enclosed—as in a police whistle—it interferes with the air vibration, causing a warbling sound. In a slide whistle (piston flute, or Swanee whistle), the lower end consists of a sliding stopper, allowing change of pitch. Longer, open flutes with the whistle's flue and lateral hole are called fipple, or whistle, flutes.