See also: Appendix:Variations of "co"
- The ISO 3166-1 two-letter (alpha-2) code for Colombia.
- (chemistry) The molecular formula for carbon monoxide.
- Abbreviation of . A state of the United States.
- Abbreviation of .
- (military) commanding officer
- (military) commissioned officer
- (US, law enforcement) corrections officer
- (geology) Initialism of .
- Abbreviation of . (Italian town in Lombardia)