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.
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.
A few languages have been reported to contrast a tap and a flap (as in the proposed definition cited above) at the same place of articulation.
Spanish features a good illustration of an alveolar flap, contrasting it with a trill: pero /ˈpeɾo/ "but" vs. perro /ˈpero/ "dog".
Among the Germanic languages, the tap allophone occurs in American and Australian English and in Northern Low Saxon.
In American and Australian English it tends to be an allophone of intervocalic /t/ and /d/, leading to homophonous pairs such as "metal" / "medal" and "latter" / "ladder" – see tapping.
In a number of Low Saxon dialects it occurs as an allophone of intervocalic /d/ or /t/; e.g. bäden /beeden/ → [ˈbeːɾn] 'to pray', 'to request', gah to Bedde!
(In some dialects this has resulted in reanalysis and a shift to /r/; thus bären [ˈbeːrn], to Berre [toʊˈbere], Warer [ˈvɑːrɜ], Varrer [ˈfarɜ].)
However, it is also possible that many of these languages do not have a lateral–central contrast at all, so that even a consistently neutral articulation may be perceived as sometimes lateral [ɺ] or [l], sometimes central [ɾ].
A velar lateral tap may exist as an allophone in a few languages of New Guinea, according to Peter Ladefoged and Ian Maddieson.
[citation needed] If other flaps are found, the breve diacritic could be used to represent them, but would more properly be combined with the symbol for the corresponding voiced stop.
In conversational (rather than carefully enunciated) speech, American English often features a nasal flap when /n/ or /nt/ are in intervocalic position before an unstressed vowel; for example, "winner" and "winter" become homophones: ['wɪ(~)ɾ̃ɚ].