O (disambiguation)

O, or o, is the fifteenth letter of the English alphabet.

O may also refer to:

Letters

 * Օ օ, (Unicode: U+0555, U+0585) a letter in the Armenian alphabet
 * Ο ο, Omicron, (Greek), a letter in the Greek alphabet
 * O (Cyrillic), a letter of the Cyrillic alphabet
 * O (kana), a romanization of the kana (お and オ) in Japanese writing
 * ㅇ, a consonant in Hangul, the Korean alphabet
 * ဝ, a consonant in Burmese script

Film and television

 * O (film), 2001 film starring Josh Hartnett, Mekhi Phifer and Julia Stiles

Literature

 * O: A Presidential Novel, anonymous novel published in 2011
 * O, fictional planet that is the setting of several short stories by science fiction author Ursula K. Le Guin
 * O, fictional character from the French erotic novel Story of O
 * "O" Is for Outlaw, the fifteenth novel in Sue Grafton's "Alphabet mystery" series, published in 1999

Media and publications

 * O, The Oprah Magazine, magazine founded by Oprah Winfrey
 * O (German magazine), a fetish magazine

Music

 * "O (Oh!)", 1920 by Ted Lewis, 1953 by Pee Wee Hunt
 * O (A.C. Acoustics album), 2002
 * O (Damien Rice album), 2002
 * O (Eiko Shimamiya album), 2006
 * O (Omarion album), 2005
 * "O" (Omarion song), the title song
 * o (Tilly and the Wall album), 2008
 * O (EP), a 2023 EP by Yuju
 * O, 2002 album by Zone
 * "O", a 2014 song by Coldplay from Ghost Stories
 * "o", a song by iamamiwhoami
 * "O!", a song by the American band Bright from The Albatross Guest House, 1997
 * O (musician), nickname of the American musician Otis Barthoulameu

Sports

 * O (gesture), a gesture used to show support for the sports teams of the University of Oregon
 * Baltimore Orioles, an American Major League Baseball team, among whose common nicknames are "O's" and "The O's"

Others

 * O (Cirque du Soleil), show at the Bellagio hotel and casino in Las Vegas, Nevada

Companies

 * Essie's Original Hot Dog shop (commonly known as "The O"), a restaurant in Pittsburgh, Pennsylvania
 * Overstock.com, online retailer previously known as O.co
 * Realty Income, American real estate investment trust (NYSE stock ticker O)

History

 * O-class battlecruiser, class of German ships in the 1930s
 * The O (political group) (The Organization), a 1970s American political group

Linguistics

 * /o/, close-mid back rounded vowel in the International Phonetic Alphabet
 * O, an antiquated vocative placed before a name of, or phrase characterizing, the party being addressed
 * O (also P), the patient-like argument (object) of a canonical transitive verb
 * O, gender neutral third person pronoun in the Turkish language
 * O-, an honorific prefix used in the Japanese language

Mathematics

 * $$f = O(g)$$, a Bachmann–Landau notation in computational complexity theory ("|f| is bounded above by g asymptotically")
 * $$f = o(g)$$, a Bachmann–Landau notation in computational complexity theory ("f is dominated by g asymptotically")
 * O, for orthogonal group
 * ∘ indicates function composition, or composition of morphisms in a category
 * Category O or $$\mathcal{O}$$, a category of Lie algebra representations
 * o, for octet, an information measure unit used in computing

Media

 * O, an IRC operator service in QuakeNet's IRC services
 * O Channel, the former name of Moji a television network in Indonesia

Places

 * O Brook, a short river in Devon, England

Science

 * Oxygen, symbol O, a chemical element
 * O, a human blood type, the universal donor
 * Haplogroup O (Y-DNA), a Y-chromosomal DNA haplogroup
 * O, for pyrrolysine an alpha amino acid in biochemistry
 * Class O, stellar classification for very hot bluish stars
 * O (for Octavius, meaning an eight of a gallon), an apothecary's symbol for a pint

Surname

 * O (surname), Korean surname romanized "O" or "Oh"
 * Ō (Japanese surname), Japanese surname derived from the Chinese surname Wang (王)
 * Ō clan a historical Japanese clan with an unrelated surname
 * Ou (surname), Chinese and Cantonese surnames pronounced "O" or "Oh"
 * A prefix meaning "grandson (of)", appearing in Irish surnames
 * Genovevo de la O (1876-1952), Mexican revolutionary
 * Karen O, born Karen Lee Orzolek, American singer

Other uses

 * Oreo O's, an American breakfast cereal available internationally
 * Oscar, the military time zone code for UTC−02:00: List of military time zones
 * JRW kinki-O.svg, the official West Japan Railway Company service symbol for the Osaka Loop Line.