A vowel is a sound in spoken langage (or a letter of the alphabet denoting such a sound) that has a sounding voice (vocal sound) of its own. Unlike a non-vowel (consonant), a vowel can be sounded on its own.
In the Roman alphabet the vowels are A,E,I,O,U and sometimes Y.
Vowels support the neighbouring consonants, but bear little information themselves (cn y rd ths?). Because of this, some alphabets (called abjads) do not represent vowels at at all.