O (disambiguation)

Look up -o, o, O, or o- in Wiktionary, the free dictionary.

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

O may also refer to:

Letters

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

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"

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/, 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

$f=O(g)$ , 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

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.