phoneme
noun [ C ] phonetics specialized uk/ˈfəʊ.niːm/ us/ˈfoʊ.niːm/
音位，音素
one of the smallest units of speech that make one word different from another word
The difference between "pin" and "pan" depends on the vowel, i.e. the different phonemes /ɪ/ and /æ/. pin和pan的不同在于元音，即音素 /ɪ/ 与 /æ/ 的不同。
Compare: grapheme