Vowel
From KneeQuickie
A vowel is usually interpreted as a sound produced by the vibration of the vocal chords with very little or no restriction of airflow. Vowels are principally classified in terms of height, frontness and rounding; in some languages the presence or absence of nasal airflow forms a separate class of nasal vowel phonemes.
The word "vowel" can also refer to a sound forming the nucleus of a syllable, whether this is a vowel by the first definition or not. Consonants (by the first definition) that form the nucleus of a syllable can alternatively be called syllabic consonants.
Also, a vowel can be a letter representing a vowel in orthography. Thus, English is said to have five orthographic vowels (and one half-vowel, Y), though it has many more than five vowel phonemes.
All languages have vowels; the fewest known vowels in a natlang is two, and the most is nearly 50. The most commonly occurring vowels are /a/, /i/ and /u/. See also vowel system.
