Phoneme

In the linguistic functionalism of the Prague School and the work of Jakobson, a phoneme is defined as a phonological unit with a distinctive function that cannot be broken down into smaller units with similar functions.

A phoneme is defined by its distinctive features, such as its being voiced (/v/) or non-voiced (/f/).

the list of phoenemes making up any given language is a closed list; Castilian employs twenty-four phonemes.