| Acronym | Definition |
|---|
| NIO | Nicaragua Córdoba (ISO currency code) |
| NIO | Northern Ireland Office |
| NIO | National Institute of Oceanography |
| NIO | Nickel Oxide (chemical compound) |
| NIO | Nicht in Ordnung (German: Not in Order; production) |
| NIO | New Input Output |
| NIO | Non-Blocking Input Output |
| NIO | National Intelligence Officer |
| NIO | Nuveen Insured Municipal Opportunity Fund Inc. (Nuveen Investments) |
| NIO | New Input/Output |
| NIO | Neurotechnology Industry Organization (San Francisco, CA) |
| NIO | Nickelore Limited (Australia) |
| NIO | Northern Illawarra Online (Australia) |
| NIO | Native Input Output |
| NIO | Network Input Output |
| NIO | Nioki, Zaire (airport code) |
| NIO | Naval Inspector of Ordnance |
| NIO | Navigational Information Office (US Navy) |
| NIO | Network for Intercultural Onomastics (name etymology and naming practices) |
| NIO | Network Information Operation |
| NIO | Netzwerk Interferenz-Onomastik (German: Network Interference-Onomastics; name etymology and naming practices) |
| NIO | Not in Office (political designation) |