The way in which an individual pronounces words depends firstly on the basic units of sound (phones) that they use in their language. The branch of linguistics which studies these units of sound is phonetics. Phones which play the same role are grouped together into classes called phonemes; the study of these is phonemics.
See also: Language, List of words of disputed pronunciation, List of words commonly mispronounced, Mispronunciation, Initial-stress-derived nounLingusitic terminology