What is the meaning of Vowel?

A sound produced by the vocal cords with relatively little restriction of the oral cavity, forming the prominent sound of a syllable.

A letter representing the sound of a vowel; in English, the vowels are a, e, i, o, u, y.

To add vowel points to a consonantal script (e.g. niqqud in Hebrew or harakat in Arabic).

Source: wiktionary.org