Each sound that you hear in a word is a Phoneme. It’s the smallest unit of sound that makes up a complete word. This is not to be confused with the letter itself; Phonemes are only the sounds made.
There are 44 Phonemes in the English language, consisting of 24 consonant sounds and 20 vowel sounds. Think of the different combinations of consonants and vowels (like “ch” or “ea”) that make unique sounds.
