One of the realisations of a phoneme. Phonemes are realised differently in different positions. Depending on the other sounds occurring in the phonetic context, these different realisations of a phoneme are called the allophones of the phoneme. This may be illustrated based on the phoneme /p/ (voiceless bilabial stop) that is realized in either an unaspirated or an aspirated variant in different phonetic environments in English. For example, after a voiceless alveolar fricative in a word such as 'spin' or at the end of the syllable in a word such as 'stop', it is realized in its unaspirated variant. Syllable-initially in a word such as 'pin' and other such contexts, it is realized in its aspirated variant.

The term allophone derives from the Greek 'allos' meaning 'other' and 'phone' meaning 'sound'.