Allophone

An allophone is a pronunciation variant of a phoneme that does not distinguish words in a language. Its distribution may depend on phonetic context or other factors.

Complementary distribution: A pattern in which two forms occur in mutually exclusive environments. Allophones in complementary distribution appear in different phonetic contexts.
Phoneme: A sound category in a language whose contrast with another category can distinguish words. An allophone is a pronunciation variant belonging to a phoneme.
English aspiration: The aspiration of English voiceless stops in contexts such as stressed syllable onsets. The aspirated and unaspirated stops are familiar context-conditioned allophones.
Phonemic contrast: A difference between sound categories that distinguishes words in a language. Allophonic differences lack the word-distinguishing function that defines phonemic contrast.
Free variation: Variation between forms that can occur in the same environment without changing meaning. Some allophones vary in the same context rather than being assigned to separate environments.
Minimal pair: A pair of words differing in one sound in the same position and having different meanings. Minimal pairs help establish whether a sound difference is phonemic rather than allophonic.
English flapping: A process in many English varieties that realizes /t/ or /d/ as a brief tap in certain contexts. The tap pronunciation is a context-conditioned realization of underlying stop phonemes.
Phonemic merger: A sound change that causes two previously distinct phonemes to become one category. A merger changes contrasts, whereas allophony describes variants within a category.
Coarticulation: The overlapping production of neighboring speech sounds as the vocal tract moves between them. Overlapping gestures often make an allophone depend on adjacent sounds.
Phonetic feature: A property of speech sounds, such as voicing, place of articulation, or nasality. Allophones may differ in one or more phonetic features while sharing a phoneme.

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