| Abbreviation | Definition |
|---|---|
| OIMC | Oklahoma Indian Missionary Conference |
| OIS | Conference on Office Information Systems |
| OIS | Open Innovation Summit |
| OITF | Orissa Information Technology Fair |
| OLC | Ohio Leadership Conference |
| OLC | Oregon Logging Conference |
| OLCC | Orthodox Lutheran Confessional Conference |
| OMAN | IEEE Lasers & Electro-Optics Society Summer topical conference on Optical Multiple Access Networks |
| OMBC | Oregon Marijuana Business Conference |
| OMC | Offshore Mediterranean Conference |
| OMGC | Oxford Medieval Graduate Conference |
| ONLC | Oregon Nonprofit Leaders Conference |
| ONS | Offshore Northern Seas |
| ONS | Open Network Summit |
| ONS | Open Networking Summit |
| OPEC | Ohio Prevention and Education Conference |
| OPEI | Operational Programme Enterprise and Innovations |
| OPSS | Orlando Pool and Spa Show |
| ORCC | Ohio Regional Campus Conference |
| ORRF | Operational Risk Research Forum |