In phonetics, a flap or tap is a type of consonantal sound, which is produced with a single contraction of the muscles so that one articulator (such as the tongue) is thrown against another. Contrast with stops and trills The main difference between a tap or flap and a stop is that in a tap/flap there is no buildup of air pressure behind the place of articulation and consequently no release burst. Otherwise a tap/flap is similar to a brief stop. Taps and flaps also contrast with trills, where the airstream causes the articulator to vibrate. Trills may be realized as a single contact, like a tap or flap, but are variable, whereas a tap/flap is limited to a single contact. When a trill is brief and made with a single contact it is sometimes erroneously described as an (allophonic) tap/flap, but a true tap or flap is an active articulation whereas a trill is a passive articulation. That is, for a tap or flap the tongue makes an active gesture to contact the target place of articulation, whereas with a trill the contact is due to the vibration caused by the airstream rather than any active movement. Tap vs. flap Many linguists use the terms tap and flap indiscriminately. Peter Ladefoged proposed for a while that it might be useful to distinguish between them.