The others have one thing in common: they describe the difference between what is and what should be. Whereas diff is commonly used for the difference between a

The others have one thing in common: they describe the difference between what is and what should be. Whereas diff is commonly used for the difference between any two things. You could make a diff (as in using the diff program) between two feature branches with no intention of merging one into the other. To me it makes sense to have separate names for these two concepts.