A slide whistle (variously known as a swannee whistle, piston flute or less commonly jazz flute) is a wind instrument consisting of a fipple like a recorder's and a tube with a piston in it. It thus has an air reed like some woodwinds, but varies the pitch with a slide. Because the air column is cylindrical and open at one end and closed at the other, it overblows the third harmonic.
To fans of 1970s BBC children's television, the instrument will always be associated with the voices of the Clangers. The instrument also features prominently in the game of "Swannee-Kazoo" in the long-running British radio panel game, I'm Sorry I Haven't A Clue.