“Õ” or “õ” is a composition of the Latin letter “O” with the diacritic mark tilde placed above it. This diacritic mark modifies the pronunciation of the letter, often indicating a nasalized vowel sound in various languages.

The HTML entity is Õ for Õ and õ for õ.

In Emilian-Romagnol,õis used to represent [õː], e.g.savõ[saˈvõː] “soap”.

In Estonian, Õ is the 27th letter of the alphabet, positioned between W and Ä. It represents a vowel characteristic of Estonian, namely the unrounded back vowel /ɤ/, which can be close-mid back, close back, or close-mid central. Historically, this vowel was represented by the letter Ö. However, in the early 19th century, Otto Wilhelm Masing introduced the letter Õ to replace Ö, aiming to eliminate confusion between several homographs and to provide clarity on word pronunciation.

In informal writing, e.g., emails, instant messaging and when using foreign keyboard layouts where the letterÕis not available, some Estonians use the characters O or 6 to approximate this letter.

In most of Saaremaa Island,Õis pronounced the same asÖ.

In Samogitian the letterÕrepresents, as in Estonian, the unrounded back vowel /ɤ/ which is unique to Samogitian and is not found in Standard Lithuanian, this is a rather new innovation brought on by the ensuing efforts of standardising Samogitian, this letter alleviates the confusion between the 2 distinct pronunciations of the letterė.

In the Portuguese language, the symbolÕstands for a nasal close-mid back rounded vowel, also written [õ] in IPA. It is not considered an independent letter of the alphabet: the tilde is the standard diacritic for nasalization.

In the Vietnamese language, the symbol Õ represents the sound [ɔ] with creaky voice, characterized by a rising tone with a glottal break followed by a continuation of the rising tone. Additionally, Vietnamese has derived letters Ỗ/ỗ and Ỡ/ỡ, which are variations of the same sound with different diacritics.

In the Võro language, this letter is the 25th letter of the alphabet, pronounced as in Estonian.^[2]

In the Skolt Sami language, this letter is the 25th letter of the alphabet, pronounced like in Estonian.

Due to character encoding confusion, the letters can be seen on many incorrectly coded Hungarian web pages, representing Ő/ő(letter O with double acute accent). This can happen due to said characters sharing a code point in the ISO 8859-1 and 8859-2 character sets, as well as the Windows-1252 and Windows-1250 character sets, and the web site designer forgetting to set the correct code page.Õis not part of the Hungarian alphabet. The usage ofUnicodeavoids this type of problems. In Latex the option of using “~o” and “~O” exists.