The volume of something is the amount of it that there is.

The volume of an object is the amount of space that it contains or occupies.

A volume is a book.

A volume is one book in a series of books.

A volume is a collection of several issues of a magazine, for example all the issues for one year.

The volume of a radio, television, or sound system is the loudness of the sound it produces.

If something such as an action speaks volumes about a person or thing, it gives you a lot of information about them.