Allophone

In phonology, an allophone (/ˈæləfoʊn/; from the Greek ἄλλος, állos, "other" and φωνή, phōnē, "voice, sound") is one of a set of multiple possible spoken sounds, or phones, or signs used to pronounce a single phoneme in a particular language. For example, in English, [t] (as in stop [stɒp]) and the aspirated form [tʰ] (as in top [ˈtʰɒp]) are allophones for the phoneme /t/, while these two are considered to be different phonemes in some languages such as Thai and Hindi. On the other hand, in Spanish, [d] (as in dolor [doˈloɾ]) and [ð] (as in nada [ˈnaða]) are allophones for the phoneme /d/, while these two are considered to be different phonemes in English. The specific allophone selected in a given situation is often predictable from the phonetic context, with such allophones being called positional variants, but some allophones occur in free variation. Replacing a sound by another allophone of the same phoneme usually does not change the meaning of a word, but the result may sound non-native or even unintelligible. Native speakers of a given language perceive one phoneme in the language as a single distinctive sound and are "both unaware of and even shocked by" the allophone variations that are used to pronounce single phonemes.