A vowel is a speech sound which is produced without any closure or obstruction of the vocal tract.
Vowels can form syllables by themselves, or they may combine with consonants.
In the English writing system, the letters a, e, i, o, u and y can represent vowels.
The term 'vowel' is used in two ways: first, for a sound which is made with the mouth fairly open and which forms the central part of a syllable; and second, for a letter which is used to write a vowel sound, e.g. a, e, i, o, u. See also the contrasting term consonant.