| Acronym | Definition |
|---|
| OTO | Overcoming the Odds (various organizations) |
| OTO | Ordo Templi Orientis (Order of Oriental Templars) |
| OTO | One to One |
| OTO | Office to Office |
| OTO | One Time Only |
| OTO | Orthotolidine |
| OTO | Over the Opening (art exhibition; New York) |
| OTO | Outflow Tract Obstruction |
| OTO | Optical Telecommunication Outlet |
| OTO | Onderzoek en Technologische Ontwikkeling (Dutch: Research and Technological Development, aka: RTD) |
| OTO | Operations Training Officer |
| OTO | Ozarks Transportation Organization |
| OTO | Open Type Organizer (software) |
| OTO | Oil Taxation Office (UK) |
| OTO | Online Tour Operator |
| OTO | Officially Twilight Obsessed Sorority (forum) |
| OTO | Or Top Offer (classified ads) |