What is the definition of volume as one of the elements of visual arts?

In visual arts volume would be the amount of plasticity or three dimensionality that something depicted has. For example, I wouldn't say humans depicted in ancient Egyptian frescoes don't have volume, namely their bodies look extremely flat as if they were cut out of paper and glued to the surface, in contrast I would say that Adam in Michelangelo's The Creation of Adam in the Sistine chapel has volume because the figure indeed does look three dimensional and has plasticity. In other Words, volume is in visual arts used to describe how is mass treated on a painting, drawing, fresco....So Egyptian figures look like they don't have any mass, they look light, while Michelangelo's Adam looks like a massive person who carries a certain amount of weight, also he possesses a kind of fullness of body. For a figure in painting to be described as a voluminous figure it does not have to be a large in size, but has to be in possession of the mentioned mass, fullness, weight, and also a certain amount of heaviness and heftiness. (This doesn't mean that the character has to be overweight. Sometimes it is said that the viewer can 'feel' the weight of a figure. In sculpture, one usually talks about closed and opened volume. Closed volume is compact, doesn't 'interact' with the space surrounding it, that is it doesn't penetrate the space, and looks as if it has some kind of central magnet that makes everything go to the centre. An example is Henry Moore sculpture of a Butterfly in Haus der Kulturen der Welt in Berlin. An example of open volume would be Gian Lorenzo Bernini's sculpture Apollo and Daphne because the characters penetrate through the surrounding space, and the space goes through the characters, also the marble doesn't look like it is dragged to some central core but kind of 'splashes' to the outside.