Question

what is true cavity?

Answer 1

A cavity is a hole that can grow bigger and deeper over time. Cavities are also called dental caries, and if you have a cavity, it's important to get it repaired. But why would your tooth develop a hole? Blame plaque. That's a sticky, slimy substance made up mostly of the germs that cause tooth decay.

Answer 2

True body cavity means that the body cavity is a proper body cavity formed by the ideal process of formation. 
hope it helps u