Vowel

In phonetics, a vowel is a sound in spoken language, such as an English ah! or oh!, pronounced with an open vocal tract so that there is no build-up of air pressure at any point above the glottis. This contrasts with consonants, such as English sh!, which have a constriction or closure at some point along the vocal tract. A vowel is also understood to be syllabic: an equivalent open but non-syllabic sound is called a semivowel.

In all oral languages, vowels form the nucleus or peak of syllables, whereas consonants form the onset and (in languages that have them) coda. Some languages also allow other sounds to form the nucleus of a syllable, such as the syllabic l in the English word table (the stroke under the l indicates that it is syllabic; the dot separates syllables)&mdash;which, nevertheless, many still consider to have a weak vowel sound &mdash;or the r in Croatian or Serbian vrt, meaning "garden".

There is a conflict between the phonetic definition of "vowel" (a sound produced with no constriction in the vocal tract) and the phonological definition (a sound that forms the peak of a syllable). The approximants and  illustrate this conflict: both are produced without much of a constriction in the vocal tract (so phonetically they seem to be vowel-like), but they occur on the edge of syllables, such as at the beginning of the English words "yet" and "wet" (which suggests that phonologically they are consonants). The American linguist Kenneth Pike (1943) suggested the terms "vocoid" for a phonetic vowel and "vowel" for a phonological vowel, so using this terminology, and  are classified as vocoids but not vowels. However, Maddieson and Emmory (1985) demonstrated from a range of languages that semivowels are produced with a narrower constriction of the vocal tract than vowels, and so may be considered consonants on that basis.

The word vowel comes from the Latin word vocalis, meaning "vocal" ("relating to voice"). In English, the word vowel is commonly used to mean both vowel sounds and the written symbols that represent them.

Articulation
The articulatory features that distinguish different vowel sounds are said to determine the vowel's quality. Daniel Jones developed the cardinal vowel system to describe vowels in terms of the common features height (vertical dimension), backness (horizontal dimension) and roundedness (lip position). These three parameters are indicated in the schematic IPA vowel diagram on the right. There are however still more possible features of vowel quality, such as the velum position (nasality), type of vocal fold vibration (phonation), and tongue root position.