Percentage difference is usually calculated when you want to know the difference in percentage between two numbers. For this calculator, the order of the numbers does not matter as we are simply dividing the difference between two numbers by the average of the two numbers.
The difference between two things is the way in which they are unlike each other.
the degree to which one person or thing differs from another: [countable; usually singular] The difference in their ages is about six months. [uncountable] There isn't much difference between one politician and another.
In context, 'difference' is often used to specify what makes two or more things distinct, whereas 'different' is applied directly to an object or concept to indicate that it is not identical to another. 'Difference' can also imply a numerical distinction, as in mathematics or measurements.