| Abbreviation | Definition |
|---|---|
| CGRS | Columbus Garden Railway Society |
| CH | Competition Header |
| CHA | Craft and Hobby Association |
| CHAV | Council House Associated Vermin |
| CHDA | Calgary Highland Dancing Association |
| CHRA | Canberra Hot Rod Association |
| CIC | Coin Inlayed Chip |
| CIS | Cruising In Style |
| CJ | Camera Jockey |
| CJ | Contact Juggling |
| CK | Collecting Knot |
| CLO | Cat Lovers Organization |
| CLYW | Caribou Lodge Yo-Yo Works |
| CMA | Christian Motorcyclists Association |
| CMBC | Cambridge Motor Boat Club |
| CMC | Chicagoland Mustang Club |
| CMTRA | Colorado Motorcycle Trail Riders Association |
| COA | Crown Of Ages |
| COCA | Coin Op Collectors Association |
| COTD | Card Of The Day |