O or O is the 15th letter in the Basic Latin alphabet of ISO and the fourth vowel in the modern English alphabet. Its English name is O (pronounced / ˈ o ʊ /), plural.

From the age of Phoenician to today, its graphic form has been quite stable. The name of the Phoenician letter is ʿ eyn, which means "eye". In fact, its shape is only from the picture of the human eye (probably inspired by the corresponding Egyptian hieroglyphs, see the original letter of faith). Its original sound value is a consonant, probably [ʕ], which is represented by the same Arabic letter letter letterayn.

This Phoenician letter is used for vowels because the early Greek letters used the letter O as "Omicron" to represent vowels / O /. This value is used in older italics, including earlier Latin letters. In Greek, there was a formal variation to distinguish between the long (omega for "Big O") and the short (Omicron for "small o"). Greek Omicron produced the corresponding Cyrillic letter O and the early italicized letter run.

Even letters that do not originate from Semitic tend to have similar forms to represent this sound. For example, the creators of the afaka and ol chiki scripts, which were invented in different parts of the world in the last century, attributed the vowel "O" to the shape of the mouth when the sound was made.

The letter "OO" is the fourth common letter in the English alphabet. [2] Like other English vowels, it has associated "long" and "short" pronunciations. In fact, the "long" shape on a ship is usually a binary / O ʊ / (it is dialectically realized anywhere from [O] to [ə]. In English, there is also a "short" ⟨ o, such as fox / ɒ /, which sounds slightly different in different dialects. In most British English dialects, it is either an open middle back round vowel [ɔ], or an open middle round vowel [;]; in American English, the most common is a round [or] to central vowel [a].

Common binary letters include ⟨ OO ⟩ for / u ː / or / ʊ; oi ⟩ or ⟨ oy ⟩ which usually means diphthong / ɔ ɪ /, andao ⟩, ⟨ OE ⟩ and Andou ⟨ depending on the context and etymology, indicating various sounds.

In other cases, especially before the letter with the smallest letter, "OO" may mean sound / ʌ /, such as "son" or "love". It can also represent semivowels / w /, such as chorus or quinoa.

In English, the isolated letter ⟨ o ⟩ which usually precedes the capitalized noun indicates the corresponding situation, such as the title of O Canada or O Captain! My captain! Or some Bible scriptures.