Phoneme
Phoneme is one of the smallest units of speech that make one word different from another word.
Phoneme is one of the set of speech sounds in any given language that serve to distinguish one word from another. A phoneme may consist of several phonetically distinct articulations, which are regarded as identical by native speakers, since one articulation may be substituted for another without any change of meaning. Thus / p/ and / b/ are separate phonemes in English because they distinguish such words as pet and bet, whereas the light and dark / l/ sounds in little are not separate phonemes since they may be transposed without changing meaning.
Meaning of phoneme in English. Cambridge Dictionary. (1995). Cambridge University Press. Retrieved from: bit.ly/47Up5SN
Phoneme definition and meaning. Collins English Dictionary. (1979). HarperCollins Publishers, Retrieved from: https://www.collinsdictionary.com/dictionary/english/phoneme