The letter was derived from the Semitic 'Ajin which represented a consonant, probably the pharyngeal consonant (IPA ) similar to the Arabic letter ع called 'Ajn', but in Greek (Omicron), Etruscan and Latin it came to be used for the vowel .

Oscar represents the letter O in the NATO phonetic alphabet. In the International phonetic alphabet, [o] represents the close-mid back rounded vowel.

In medicine, O (also, O+ or O-) is one of the human blood types.

In chemistry, O stands for oxygen.

O is also a symbol for a hug, as in love notes. (See Hugs and Kisses.)

O is also the nickname of a magazine founded by Oprah Winfrey, more formally called O, The Oprah Magazine.

O may refer to the 2002 album by Damien Rice, see O (album)

O is also a movie.

O is a family name in Japanese; see O (name).

Story of O is a French erotic novel.

In economics, O is usually used to represent output.

See also