The word flute can mean many different instruments, which all have the common characteristic that they create sound by the means of an airstream which is broken over an edge. This produces a repeating cycle of turbulence (via the Bournelli Effect), which sets an enclosed column of air in motion, The entire column of air from the end of the flute to the first open tone hole vibrates as a unit, a phenomenon called a standing wave. This produces sound.
The flute is the oldest--and in its basic form, the simplest--instrument of the woodwind family. Flutes have existed since before written history. The oldest known flute we have recovered was made from a cave bear femur bone fragment, and is estimated at between 40,000 to 80,000 years old, possibly having been created and played by Neanderthal Man.
There are many different types of flutes found the world over, from the simplest folk flutes, to the elaborately complex instruments found in today's bands and orchestras.
In Western music, the word flute refers to instruments of two broad families, the transverse flutes, which are played held horizontally to the body and which have no fixed windway, and the fipple flutes, such as the [whistle] and the [recorder], which are held vertically and which do have a fixed windway, requiring no special embouchure (or shaping of the lips) by the player.
This is an old [Conn] flute made in 1920 that I'm restoring.
My collection includes a number of different kinds of flutes; please click on the boxes, above, to see photos and hear recordings of the various instruments.