| Acronym | Definition |
|---|
| UO | University of Oregon |
| UO | Ultima Online (game) |
| UO | Urban Outfitters |
| UO | Uh Oh |
| UO | Universal Orlando (Orlando, Florida) |
| UO | University of Oxford |
| UO | University of Oklahoma |
| UO | Underoath (band) |
| UO | University of Ottawa |
| UO | Urban Operations (game) |
| UO | Urge Overkill (band) |
| UO | University of Otago (New Zealand) |
| UO | University Outreach |
| UO | Urinary Output |
| UO | Unusual Occurrence |
| UO | Unexploded Ordnance |
| UO | Undercover Officer |
| UO | Université d'Orléans (French: University of Orleans) |
| UO | Uru Obsession (website) |
| UO | Unit Operator |
| UO | Uncle Owen (Star Wars character) |
| UO | Union Railroad of Oregon |
| UO | Official Envelope (Scott Catalogue prefix; philately) |
| UO | Under-Officer |
| UO | Undelivered Orders |
| UO | ureteric orifice |