| Abbreviation | Definition |
|---|---|
| NTC | National Tennis Center |
| NTF | Nigeria Tennis Federation |
| NTRP | National Tennis Rating Program |
| NTRP | National Tennis Ratings Program |
| NTTF | Nigeria Table Tennis Federation |
| NWTA | Northwest Wheelchair Tennis Association |
| OBTA | Orange Blossom Tennis Association |
| OBTA | Orange Blossom Tennis Association (Orlando, FL) |
| ODTA | Oahu District Tennis Association |
| OIBM | Offene Internationale Bayerische Meisterschaft (in German) Open International Bavarian Championship |
| OLTA | Oak Lawn Tennis Association |
| OLTC | Oegstgeester Lawn Tennis Club |
| OPTA | Oak Park Tennis Association |
| OPTC | Oak Park Tennis Center |
| OTA | Ontario Tennis Association |
| OTA | Ontario Tennis Association's |
| OTC | Other Tennis Club |
| OTTA | Ontario Table Tennis Association |
| OTTA | Otago Table Tennis Assn |
| OTTC | Ottawa Table Tennis Club |