An open vowel is a vowel sound of a type used in most spoken languages. The defining characteristic of an open vowel is that 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. The open vowels identified the International Phonetic Alphabet are:

• open front unrounded vowel [a]
• open front rounded vowel [ɶ]
• open back unrounded vowel [ɑ]
• open back rounded vowel [ɒ]

In the context of the phonetics 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.