Question

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

Answer 1

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.

Answer 2

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.
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