cavity

Short definition from Wiktionary

Noun

1. 1
   A hole or hollow depression in a solid object: A hollow area within the body.
2. 2
   A hole or hollow depression in a solid object: The female part of a mold: the depression itself or (metonymically) the half of the mold that contains it.
3. 3
   A small or large hole in a tooth caused by caries; often also a soft area adjacent to the hole also affected by caries.