That's the correct definition of "disposable income". The latter value is called "discretionary income", and a lot of people incorrectly say disposable when they really mean discretionary.

It’s always cases like this that make question if the dictionary is wrong, or if everyone speaking the language is wrong.

Yeah it’s hard to calculate a comparable figure on this when savings in one country is basically just temporarily holding money for the medical industry and getting to collect gains on it in the meantime, and in another, it’s actual savings.