In phonetics and linguistics, a phone is any distinct speech sound or gesture, regardless of whether the exact sound is critical to the meanings of words. In contrast, a phoneme is a speech sound that, in a given language, if it were swapped with another phoneme, would change the meaning of the word. Phones are absolute, not specific to any language, but phonemes can be discussed only in reference to specific languages.
For example, the English words kid and kit end with two distinct phonemes, and swapping one for the other would change the word's meaning. However, the difference between the p sounds in pun (pʰ, with aspiration) and spun (p, no aspiration) never affects the meaning of a word in English so they are phones and not phonemes. By contrast, swapping the same two sounds in Hindi or Urdu can change one word into another: pʰal means 'fruit', and pal means 'moment' (CIIL 2008).
In the context of spoken languages, a phone is an unanalyzed sound of a language (Loos 1997). A phone is a speech segment that possesses distinct physical or perceptual properties and serves as the basic unit of phonetic speech analysis. Phones are generally either vowels or consonants.
A phonetic transcription (based on phones) is enclosed within square brackets ([ ]) rather than the slashes (/ /) of a phonemic transcription (based on phonemes). Phones (and often phonemes also) are commonly represented using symbols of the International Phonetic Alphabet (IPA).
For example, the English word spin consists of four phones, [s], [p], [ɪ] and [n], and thus it has the phonetic representation [spɪn]. The word pin has three phones; in that word, the initial sound is aspirated and so can be represented as [pʰ]; the word's phonetic representation would then be [pʰɪn]. (Precisely the features shown in a phonetic representation depends on whether a narrow or broad transcription is being used the features that the writer wishes to draw attention in the context.)
When phones are considered to be realizations of the same phoneme, they are called allophones of that phoneme (more information on the methods of making such assignments can be found under phoneme). In English, for example, [p] and [pʰ] are considered allophones of a single phoneme, written as /p/. The phonemic transcriptions of the above two words is consequently /spɪn/ and /pɪn/, aspiration no longer being shown since it is not distinctive.