Open-mid back rounded vowel in the context of "Vowel height"

Omega (US: /oʊˈmeɪɡə, -ˈmɛɡə, -ˈmiːɡə/ , UK: /ˈoʊmɪɡə/; uppercase Ω, lowercase ω) is the twenty-fourth and last letter in the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The name of the letter was originally ὦ (ō̂ [ɔ̂ː]), but it was later changed to ὦ μέγα (ō̂ méga 'big o') in the Middle Ages to distinguish it from omicron ⟨ο⟩, whose name means 'small o', as both letters had come to be pronounced [o]. In modern Greek, its name has fused into ωμέγα (oméga).

In phonetic terms, the Ancient Greek Ω represented a long open-mid back rounded vowel [ɔː], in contrast to omicron, which represented the close-mid back rounded vowel [o], and the digraph ⟨ου⟩, which represented the long close back rounded vowel [uː]. In modern Greek, both omega and omicron represent the mid back rounded vowel [o̞]. The letter omega is transliterated into a Latin-script alphabet as ō or simply o.

Omicron (US: /ˈoʊmɪkrɒn, ˈɒmɪkrɒn/ , UK: / oʊˈmaɪkrɒn/; uppercase Ο, lowercase ο, Greek: όμικρον) is the fifteenth letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the close-mid back rounded vowel [o] in contrast to omega, which represented the open-mid back rounded vowel [ɔː], and the digraph ⟨ου⟩ which represented the long close back rounded vowel [uː]. In modern Greek, both omicron and omega represent the mid back rounded vowel [o̞]. Letters that arose from omicron include Roman O and Cyrillic O and Ю. The name of the letter was originally οὖ (oû [ûː]), but it was later changed to ὂ μικρόν (ò mikrón 'small o') in the Middle Ages to distinguish the letter from omega ⟨ω⟩, whose name means 'big o', as both letters had come to be pronounced [o]. In modern Greek, its name has fused into όμικρον (ómikron). In the system of Greek numerals, it has a value of 70.

Open o or turned c (majuscule: Ɔ, minuscule: ɔ) is a letter of the extended Latin alphabet. In the International Phonetic Alphabet, it represents the open-mid back rounded vowel. It is used in the orthographies of many African languages using the African reference alphabet.

The Yucatec Maya language used Ɔ to transcribe the alveolar ejective affricate [t͡sʼ] consonant in the orthography of the Colonial period. Now dz or tsʼ is preferred.

The phonology of Bengali, like that of its neighbouring Eastern Indo-Aryan languages, is characterised by a wide variety of diphthongs and inherent back vowels (both /o/ and /ɔ/).