CO

CO or variants may refer to:

Chemistry

 * Carbon monoxide (CO), a colorless, odorless, and tasteless gas
 * Carbonyl group, composed of a carbon atom double-bonded to an oxygen atom: C=O
 * Cobalt, a chemical element, symbol Co

Computing and telecommunications

 * .co (second-level domain), the Internet second-level domain meaning "commercial"
 * .co, the Internet country code top-level domain (ccTLD) for Colombia
 * Commitment ordering (CO), a concurrency control technique for databases
 * Telephone exchange, or central office (CO)

Mathematics

 * Cofunction, or Co, in trigonometry
 * Cuboctahedron, a uniform polyhedron

People

 * Nguyễn Hữu Có (1925–2012), Vietnamese general
 * Conrado Co (born 1940), Filipino badminton player
 * Alfredo Co (born 1949), Filipino Sinologist
 * Atoy Co (born 1951), Filipino actor and basketball coach
 * Leonard Co (1953–2010), Filipino botanist
 * Nando Có (born 1973), Bissau-Guinean footballer
 * Kenedy Có (born 1998), Bissau-Guinean footballer
 * Samuel S. Co, Filipino politician

Places

 * CO postcode area, or Colchester postcode area, England
 * Colombia, ISO 3166-1 country code CO
 * Colorado, United States postal abbreviation CO
 * Counties of Ireland, abbreviated Co.

Ranks and titles

 * C.O., post-nominal initials of members of the congregation of the Oratory of Saint Philip Neri
 * C/O, cadet officer ranks of the Junior Reserve Officers' Training Corps
 * Commanding officer (CO), the officer in command of a military unit
 * Contracting Officer (CO or KO), in the U.S. government
 * Correctional officer (CO), an officer whose duty it is to safeguard and promote the welfare of inmates
 * Circle officer (CO), in the Indian government
 * Conscientious objector

Transportation

 * Chemins de fer Orientaux (CO), a former Ottoman railway company
 * Chesapeake and Ohio Railway (C&O or CO), a former American railroad
 * Cobalt Air (IATA airline designator CO, 2016-2018), a Cypriot airline
 * Continental Airlines (IATA airline designator CO, 1937-2012), an American airline

Other uses

 * co-, an English prefix meaning coming together
 * Cardiac output (CO), the volume of blood being pumped by the heart per time unit
 * Castres Olympique, a French rugby club
 * Certificate of occupancy (CO), a legal document
 * Certificate of origin (often abbreviated to C/O or CoO), in international trade
 * Company, abbreviated co.
 * Corsican language, ISO 639-1 language code co
 * ℅, a Unicode character in the Letterlike Symbols block
 * c/o, former name of Gerhardsen Gerner, an art gallery in Berlin