A phoneme is a single, distinct unit of sound in speech that provides the basis for forming complete words and sentences. A phoneme has no inherent meaning by itself, but when multiple phonemes are combined in different ways, they create meaningful words.
The English alphabet has 26 letters but about 40 phonemes. This means that letters combine in different ways to represent the various sounds a person can make while speaking. These sounds help to distinguish the meanings of words. It is possible to break down each word into its constituent phonemes to understand the various sounds within that word. However, the best way to learn and improve pronunciation is to actually say the word out loud and focus on its sound, rather than its phonemic representation on paper.
A phoneme is represented by one or more letters placed between forward slashes at either end, as per the rules and standards set by the International Phonetic Alphabet. The pronunciation of a phoneme can be different, depending upon the accent of different speakers. These differing pronunciations are known as ‘allophones’ and they do not change the inherent meaning of the word itself. There are approximately 20 vowel phonemes and 25 consonant phonemes, with slight variations due to different dialects and interpretations.