What is the definition of Volume?

Volume V (l, m³, cm³)
The term volume is used to designate:
a) the purely geometric, 3-dimensional,usually predetermined, space filling content of a vacuum chamber or a complete vacuum system including all the piping and connecting spaces (this volume can be calculated);
b) the pressure-dependent volume of a gas or vapor which, for example, is moved by a pump or absorbed by an adsorption agent.