Speech is the spoken medium of language.
Phonology is a branch of linguistics.
It is concerned with the study of the sound systems of languages. The aims of phonology are to demonstrate the patterns of distinctive sound contrasts in a language, and to explain the ways speech sounds are organised and represented in the mind. The gradual process of acquiring adult speech patterns is called phonological development. Putting it another way, the emergence in children of a properly organised speech sound system is called phonological development. Table 1 provides a rough rule of thumb for how clearly your child should be speaking, bearing in mind that there is considerable individual variation between children.