The mid back rounded vowel is a type of vowel sound, used in some spoken languages. While there is no dedicated symbol in the International Phonetic Alphabet that represents the exact mid back rounded vowel between close-mid [o] and open-mid [ɔ], it is normally written ⟨o⟩. If precision is desired, diacritics may be used, such as ⟨o̞⟩ or ⟨ɔ̝⟩, the former being more common.

Multiple para-IPA alternative symbols also exist for this vowel. The Swedish Dialect Alphabet uses the symbol ⟨ⱺ⟩ (an o with low ring), while Sinological notation uses the symbol ⟨o̧⟩ (an o with cedilla). The symbol ⟨ꭥ⟩ (a small capital omega) was proposed for Americanist notation, but was never implemented.

Just because a language has only one non-close non-open back vowel, it still may not be a true-mid vowel. Tukang Besi is a language in Sulawesi, Indonesia, with a close-mid [o]. Taba, another language in Indonesia, in the Maluku Islands, has an open-mid [ɔ]. In both languages, there is no contrast with another mid (true-mid or close-mid) vowel.

Kensiu, in Malaysia and Thailand, is highly unusual in that it contrasts true-mid vowels with close-mid and open-mid vowels without any difference in other parameters, such as backness or roundedness.