OB: See Outside Broadcast.
Off-Line: Out of action, not currently useable.
Off-Line Edit: A "draft" edit, usually prepared in an off-line edit suite (at a lower cost), then taken to an on-line facility to make the final cut. Related info: Video Editing
On-Line (1): Operational.
On-Line (2): In multi-camera or multi-tape set-ups, the camera or videotape machine which is currently selected by the director. For example, in an outside broadcast, the on-line camera is the camera which is currently live.
On-Line Edit: The final version of an edit, prepared in a professional edit facility.
Optical: Of light/optics.
Optical Image Stabiliser (OIS): A system of stabilizing a camera image by constantly adjusting the optics.
Optical Zoom: A method of zooming which uses a telephoto lens, i.e. the zoom is provided by the optics rather than digital processing. Optical zoom is better than digital zoom More info: Digital vs optical zoom
Optics: Dealing with properties of light. Camera optics: The components which deal with light rays, before they are converted into electrical signals (i.e. the lens, etc).
Oscilloscope: Device which accepts an electrical input, and represents the variations of the input as a display on a CRT screen. More Info: Oscilloscope
Outside Broadcast: A radio or television program which is broadcast from location, rather than from a studio. More info: Outside Broadcast