1. Aspect ratio convertor (pronounced "arc" not A.R.C.), used to convert pictures from one aspect ratio to another, for instance to convert 4:3 archive footage so it can be included in a 16:9 widescreen programme.  Arc is used sometimes as a verb, eg: "these pictures need to be ARCed".

2. Arc is also a type of powerful lamp used in the film industry.

3. Sometimes Arc might also describe the panning movement of a camera on a crane or jib arm.