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 (2001 film), a film starring Josh Hartnett, Mekhi Phifer and Julia Stiles
- O (2022 film), an Indian Kannada-language horror thriller film
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
- 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)
- O-class battlecruiser, class of German ships in the 1930s
- The O (political group) (The Organization), a 1970s American political group
- /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
- f = O ( g ) {\displaystyle f=O(g)} , a Bachmann–Landau notation in computational complexity theory ("|f| is bounded above by g asymptotically")
- f = o ( g ) {\displaystyle 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 O {\displaystyle {\mathcal {O}}} , a category of Lie algebra representations
- o, for octet, an information measure unit used in computing
- O, an IRC operator service in QuakeNet's IRC services
- O Channel, the former name of Moji a television network in Indonesia
- O Brook, a short river in Devon, England
- 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
- 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
- Oreo O's, an American breakfast cereal available internationally
- Oscar, the military time zone code for UTC−02:00: List of military time zones#O
- , the official West Japan Railway Company service symbol for the Osaka Loop Line.
- All pages with titles beginning with O
- All pages with titles containing O
- Mr. O (TV show)
- Circle (disambiguation)
- Circle symbol (disambiguation)
- Zero (disambiguation)
- Big O (disambiguation)
- Omicron (disambiguation) including Ο/ο
