| Acronym | Definition |
|---|
| OSI | Open Systems Interconnection |
| OSI | Office of Special Investigations |
| OSI | Open Society Institute |
| OSI | Open Source Initiative |
| OSI | Online Software |
| OSI | Office of Strategic Influence (band) |
| OSI | Open Systems International (Minneapolis, MN) |
| OSI | Osram Sylvania Inc. |
| OSI | Open System Interface |
| OSI | Outsourcing Solutions Inc. |
| OSI | Outback Steakhouse, Inc. |
| OSI | Out of Stock Indefinitely (usually referring to books) |
| OSI | Options Symbology Initiative (Options Clearing Corporation) |
| OSI | On-Site Inspection |
| OSI | Office of Scientific Intelligence |
| OSI | Office of Science and Innovation |
| OSI | Office of Strategic Initiatives |
| OSI | Office of Scientific Investigation (aka Office of Scientific Intelligence; fictional agency; Six Million Dollar Man and Bionic Woman) |
| OSI | Open Systems, Inc. |
| OSI | Office of School Improvement |
| OSI | Office of Strategic Information |
| OSI | Objective Systems Integrators, Inc. |
| OSI | Office of Secret Intelligence (fictional, Venture Brothers) |
| OSI | Office of Scientific Information |
| OSI | Other Similar Incidents |
| OSI | Open Switching Interval |
| OSI | Open System Integration |
| OSI | Ontario Swine Improvement Inc. (Ontario, Canada) |
| OSI | Ounces per Square Inch |
| OSI | Other Supplemental Information |
| OSI | Operator System Interface |
| OSI | Open Systems Interoperability |
| OSI | Open Standard Interconnection |
| OSI | Office of Statewide Intelligence (FDLE) |
| OSI | Optical Storage International |
| OSI | Operations System Interface |
| OSI | Operating Space Item |
| OSI | Organizational Strategies, Inc. (Arlington, VA) |
| OSI | Origin Systems Incorporated |
| OSI | Other Security Interests |
| OSI | Occupational Stress Injury (psychological difficulty) |
| OSI | Offshore Systems, Inc |
| OSI | operational subsystem interface (US DoD) |
| OSI | Operational Support Inventory |
| OSI | Online Social Interaction |
| OSI | Optimum Source Impedance |
| OSI | Originating Station Identifier |
| OSI | One Side Installation |
| OSI | Congregatio Oblatorum Sancti Ioseph (religious order, Oblates of St. Joseph) |
| OSI | Origo Sino-India PLC (UK) |
| OSI | Outsourcing Services India |
| OSI | Operating System Independent (computing) |
| OSI | Oponix Systems Inc. |