| Abbreviation | Definition |
|---|---|
| ODCS | Open Door Christian Schools |
| ODCS | Ottawa Dance Centre Schools |
| ODIS | Organisation to Decolonise International Schools |
| ODSS | Orangeville District Secondary School |
| ODTS | One Day Traffic School |
| OECS | Oppenheim Ephratah Central School |
| OEHS | Oswego East High School |
| OEHS | Otto Eldred High School |
| OES | Oakstead Elementary School |
| OES | Oakville Elementary School |
| OES | OETI Engineering School |
| OES | Ooltewah Elementary School |
| OFCS | Olmsted Falls City Schools |
| OFGS | Oxford Falls Grammar School |
| OFHS | Orchard Farm High School |
| OFIS | Olmsted Falls Intermediate School |
| OFIS | Ontario Federation of Independent Schools |
| OFMS | Olmsted Falls Middle School |
| OFS | Overseas Family School |
| OFSAA | Ontario Federation of Schools Athletic Association |