An open vowel is a vowel sound in which the tongue is positioned as far as possible from the roof of the mouth. Open vowels are sometimes also called low vowels in reference to the low position of the tongue.

In the context of the phonology of any particular language, a low vowel can be any vowel that is more open than a mid vowel. That is, open-mid vowels, near-open vowels, and open vowels can all be considered low vowels.