In phonetics, an allophone is one of several similar speech sounds (phones) that belong to the same phoneme. A phoneme is an abstract unit of speech sound that can distinguish words: That is, changing a phoneme in a word can produce another word. Speakers of a particular language perceive a phoneme as a distinctive sound in that language. An allophone is not distinctive, but rather a variant of a phoneme; changing the allophone won't change the meaning of a word, but the result may sound non-native, or be unintelligible. (There is debate over how real, and how universal, phonemes really are. See phoneme for details.)
Every time a speech sound is produced, it will be slightly different from other utterances. Only some of the variation is significant (i.e., detectable or perceivable) to speakers. There may be complementary allophones which are distributed regularly within speech according to phonetic environment, as well as notable free variants, which are a matter of personal habit or preference. Not all phonemes have significantly different allophones.
In the case of complementary allophones, each allophone is used in a specific phonetic context and may be involved in a phonological process.
A tonic allophone is sometimes called an allotone, for example in the neutral tone of Mandarin.
