Question

What does it mean to talk about the 'volume' of the rectangul
ar box or cylindrical container

Answer 1

Volume is the measure amount of space inside of a solid figure like a cube, ball, cylinder or pyramid. Its units are always cubic this is the number of little element cubes that fit inside the figure.
Hope that Helped! :)
Welcome

Answer 2

Your talking about the amount of space there is within an object;
Volume only exists for 3D objects;
With 2D objects, you just have area.