The principle of all flutes is that the player blows against an edge, and the turbulence created in the attached tube generates the notes: the simplest example is blowing across the top of an empty bottle. The pitch is then determined by the length of the tube and the presence of any open holes along its length.
With the transverse flute, the strength, shape and direction of the air is controlled by the player’s lips (their “embouchure”), allowing a wide range of control over tone and dynamics. In effect the player’s lips form the windway.
With the recorder however, the windway is created by the block or fipple in the end of the instrument, which directs the air stream onto the lip. It is this fixed windway which determines the flow of air, making it relatively easy to produce notes, but allowing little variation in their characteristics.