phonology

n. Phonology is the component of a language's grammar which licenses the sound structure for sentences, phrases, or words. Phonological structure consists of a sequence of phonemes, or contrastive sounds, related to each other hierarchically: consonants and vowels are grouped into syllables; syllables are grouped into prosodic words (or phonological words); prosodic words are grouped into intonational phrases; and so on. The phonology of a language specifies what sound sequences are allowed and disallowed within and between words, by phonotactic constraints. For example, neither plarg nor tlarg is a word in English, but the sequence of initial consonants in tlarg makes it an impossible word for the language. A language's phonology also specifies the phonemic inventory, the collection of distinctive sounds for that language. Finally, a language's phonology contains principles used to transform a phonological representation into its surfacing phonetic form. For example, in American English, the underlying phoneme /t/ at the end of the morpheme write surfaces, by phonological rule, as a flap [R] in writing, as an unaspirated stop [t] in writes, and possibly as unreleased [t?] in write. – EMF

▶ See also PHONEME and PROSODY