cavity

(KA-vih-tee) A hollow area or hole. It may describe a body cavity (such as the space within the abdomen) or a hole in a tooth caused by decay.

A hole or hollow area, especially inside a tree. Many animals, such as woodpeckers and raccoons, live in them.

A volume defined by conductor-dielectric or dielectric-dielectric reflective boundaries, or a combination of both, and having dimensions designed to produce specific interference effects (constructive or destructive) when excited by an electromagnetic wave.