| OFC/OFN | Designation of Fiber Optic cable which meets Steiner Tunnel test |
| OFCR/OFNR | Designation of Riser Fiber Optic cable which meets Riser flame test |
| Ohm | Unit of resistance such that a constant current of one ampere produces a force of one volt |
| OSHA | Abbreviation for Occupation Safety and Health Act. Specifically the Williams-Steiger law passed in 1970 covering all factors relating to safety in places of employment |
| Overall Diameter | Finished diameter over wire or cable |
| Overcoat | Individual strands of tin copper wire stranded together and then covered with a tin coating |
| Overlap | The amount the trailing edge laps over the leading edge of a tape wrap |
| Oxygen Index | Percentage of oxygen necessary to support combustion of a specified material |
| Ozone | A highly active form of oxygen produced by the passage of electric discharges or sparks through air or oxygen |
