| Acronym | Meaning |
| CO | Central Office (telecommunications/telephony) |
| CO | Commanding Officer |
| CO | Cabinet Office |
| CO | Case Operations |
| CO | Certifying Officer |
| CO | Chief Operator |
| CO | Circle Officer (India) |
| CO | Clerical Officer (obsolete, now AO) |
| CO | Colchester (postcode, United Kingdom) |
| CO | Collection Officer |
| CO | Colonial Office (UK) |
| CO | Combat Aptitude Area |
| CO | Command |
| CO | Command Operations |
| CO | Commissioned Officer |
| CO | Communications Officer |
| CO | Compliance Order |
| CO | Conscientious Objector |
| CO | Consent Order |
| CO | Conservation Operations |
| CO | Consolidated Obligation |
| CO | Contracting Officer |
| CO | Contracting Official |
| CO | Correctional Officer |
| CO | Course |
| CO | Current Operations |
| CO | Custodial Officer |