| Acronym | Definition |
|---|
| IOI | International Olympiad in Informatics |
| IOI | Island of Ireland |
| IOI | Interest on Investment (finance) |
| IOI | Innovative Online Industries |
| IOI | International Ocean Institute |
| IOI | Indian Ocean Islands |
| IOI | Institute of Informatics (various locations) |
| IOI | Indicator of Interest |
| IOI | International Ombudsman Institute (Canada) |
| IOI | Indication of Interest |
| IOI | Interuniversitair Oogheelkundig Instituut (Dutch) |
| IOI | Independent Opportunities, Inc. (Tulsa, OK) |
| IOI | Innovations in Optics, Inc. (Woburn, MA) |
| IOI | Identity of Interest |
| IOI | Item of Interest |
| IOI | Interonset Interval (music composition) |
| IOI | Israel Opportunity Investor (blog) |
| IOI | In Orbit Infrastructure |
| IOI | Integrated Operating Instruction (specifically, how to start up or shut down a nuclear power plant) |
| IOI | Interim Operating Instructions |
| IOI | Items of Importance |
| IOI | Internal Operating Instruction |
| IOI | Inter-Ocular Impact (hits you right between the eyes) |
| IOI | Item of Inspection |
| IOI | Internal Operating Income |