The word(part) or abbreviation/acronym/initialism Co or CO has several meanings, depending on context:

• Carbon monoxide (CO) (chemical symbol)
• Care of (c/o) (postal code used for temporary address change)
• Central office (telecommunications and telephony)
• check out (co) (RCS command)
• co gender-neutral pronoun
• co- prefix (form of com-, signifying with, together, in conjunction, joint)
• Co (UIC classification of railroad locomotive wheel arrangement, known as 0-6-0 in the Whyte notation)
• Co (ethnicity) , an ethnic group in Southeast Asia
• Cobalt (Co) (ferromagnetic metallic chemical element)
• Colombia (ISO 3166-1 country code)
• Colorado (CO) (U.S. postal abbreviation)
• Commanding officer (CO) (military)
• Company (Co.) (general business abbreviation)
• Conscientious objector (military)
• Continental Airlines (IATA airline code)