| Abbreviation | Definition |
|---|---|
| UCI | United Cycling Institute |
| UCL | Ultimate Champions League |
| UCL | Unbelievably Cubs Like |
| UCLA | U Can Lose Again |
| UCPA | Union Nationale des Centres Sportifs de Plein Air |
| UCS | Ultimate Collector Series |
| UCT | Ultimo Champion Tourny |
| UCT | Underwater Camping Team |
| UCW | Ultimate Championship Wrestling |
| UD | Upper Deck |
| UDA | Universal Dance Association |
| UDA | Upper Deck Authentic sports memorabilia |
| UDFAs | Undrafted Free Agents |
| UDH | Ultimate Deer Hunt |
| UDIC | Ultima Dragons Internet Chapter |
| UDLP | Union Deportiva Las Palmas |
| UDP | Umpire Development Program |
| UDRS | Umpire Decision Review System |
| UDW | Sport Union Deutsch Wagram |
| UEFA | Union Of European Football Associations |