This page discusses a phenomenon in the phonology of English. For other uses, see Flap.

Flapping is a phonological process found in many dialects of English, especially American English and Canadian English, by which intervocalic and /d/ surface as the alveolar flap [ɾ] before an unstressed syllable. Flapping is a specific type of lenition, specifically intervocalic weakening. For people with the merger these following words sound the same or almost the same:

• matter/madder
• grater/grader
• metal/medal

The merger does not occur when an intervocalic /t/ or /d/ is followed by a syllabic 'n', so written and ridden remain distinct, nor does it occur when the /t/ or /d/ belongs to a second stressed syllable in the word, as in retail. In many accents, such words as riding and writing continue to be distinguished by the preceding vowel: though the consonant distinction is neutralized, the underlying voice distinction continues to select the allophone of the /aɪ/ phoneme preceding it. Thus for many Canadians, riding is [ɹaɪɾɪŋ] while writing is [ɹəɪɾɪŋ].

The cluster [nt] can also be flapped; the IPA symbol for a nasal flap is [ɾ̃], but articulatorily this is nothing more than an ultrashort [n]. As a result, in quick speech, words like winner and winter can become homophonous.

Flapping also occurs in other languages, such as Western Apache (and related languages). In Western Apache, intervocalic /t/ similarly is realized as [ɾ] in intervocalic position. This process occurs even over word boundaries. However, flapping is blocked when /t/ is the initial consonant of a stem (i.e. flapping occurs only when /t/ is stem-internal or in a prefix). Unlike English, flapping is not affected by suprasegmentals (i.e. stress or tone).