The retroflex flap is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɽ⟩, and the equivalent X-SAMPA symbol is ⟨r`⟩.
Features of the retroflex flap:
Its manner of articulation is flap, which means it is produced with a single contraction of the muscles so that one articulator (usually the tongue) is thrown against another.
Its place of articulation is retroflex, which prototypically means it is articulated subapical (with the tip of the tongue curled up), but more generally, it means that it is postalveolar without being palatalized. That is, besides the prototypical sub-apical articulation, the tongue contact can be apical (pointed) or laminal (flat).
Its phonation is voiced, which means the vocal cords vibrate during the articulation.
It is an oral consonant, which means air is allowed to escape through the mouth only.
It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the lungs and diaphragm, as in most sounds.
Japanese /r/ may be transcribed with ⟨ɽ⟩, in which case it represents the postalveolar flap rather than retroflex. Toda has a retroflex trill, which is transcribed with the same IPA symbol.
