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) used to pronounce a single phoneme. For example, (as in pin) and (as in spin) are allophones for the phoneme /p/ in the English language. Although a phoneme's allophones are all alternative pronunciations for a phoneme, the specific allophone selected in a given situation is often predictable. Changing the allophone used by native speakers for a given phoneme in a specific context usually will not change the meaning of a word but the result may sound non-native or unintelligible. Native speakers of a given language usually perceive one phoneme in their language as a single distinctive sound in that language and are "both unaware of and even shocked by" the allophone variations used to pronounce single phonemes.

Read more about Allophone:  History of Concept, Complementary and Free-variant Allophones, Allotone, Examples in English Vs. Other Languages, Representing A Phoneme With An Allophone