Definite volume refers to something which has a consistent, unchanging volume, which in practical terms may mean a static mass and density, or a predetermined shape, either of which will dictate volume. A cube with side length l has a definite volume because it can only be exactly one size.
One cup of raw plantains or one medium sized raw plantain contains: ~180-200 calories, 0.5 g total fat, 47-50 g carbohydrates, 3.5 g dietary fiber, 22 g sugar and 2 g protein. Because of it's high carbohydrate content, you need to monitor your portion, otherwise your blood sugars will spike.
As the peel changes to brown or black, it has a sweeter flavor and more of a banana aroma, but still keeps a firm shape when cooked. The plantain averages about 65% moisture content and the banana averages about 83% moisture content. Since hydrolysis, the process by which starches are converted to sugars, acts fastest in fruit of higher moisture content it converts starches to sugars faster in bananas than it does in plantains.