Phoneme
Phonemes are the units of sound (speech) which distinguish one word from another in a particular language. In most varieties (accents and dialects) of spoken English there are about 23 consonantal phonemes and 21 vowel phonemes (altogether 44 phonemes), but only 26 letters in writing. To see all the phonemes in English, the IPA, has a unique letter for every phoneme, unlike the English alphabet.