What are phonemes?

A phoneme is the smallest unit of sound in speech. When we teach reading we teach children 
which letters represent those sounds. For example – the word ‘hat’ has 3 phonemes – ‘h’ ‘a’ 
and ‘t’. The phoneme is what we hear.
A grapheme is a letter or a number of letters that represent the sounds in our speech. So a 
grapheme will be the letter/ letters that represent a phoneme (see above). English has a complex 
written code and in our code a grapheme can be 1, 2, 3 or 4 letters.