1. A depression or recess in a ceiling, often forming a horizontal FOH theatrical lighting position. Vertical openings are usually called slots. May also be purely decorative, and not contain any ERSs.
3D Theater Design - Pricing
2. A type of molding containing an inside curve.
Big Johnson Millwork Cove Molding page
3. The router or shaper bit used for making a cove.
Saw & Bits Online Store