Phonology
Phonology is a branch of linguistics which studies the sound systems of languages. Out of the very wide range of sounds the human vocal apparatus can produce, and which are studied by phonetics, only a relatively small number are used distinctively in any one language. The sounds are organized into a system of contrasts, which are analyzed in terms of phonemes, distinctive features or other such phonological units, according to the theory used.
Phonology deals with the ways in which sounds behave in languages, and it is a central part of linguistics.
Phonology was transformed by the introduction of distinctive features (phonological units smaller than phonemes).
David Crystal. (2008). A Dictionary of Linguistics and Phonetics, 6th Edition. (p. 365). New-Jersey: Wiley-Blackwell. Retrieved from: https://bit.ly/3Ol0rUw
Trask R.L. (1999). Key Concepts in Language and Linguistics. (p.156). London: Routledge. Retrieved from: https://bit.ly/49cffgh