(mathematics) a type of calculus in which the rate at which one variable in a situation changes in relation to another is able to be computed at any point in a process, such as a given instant in time or a givenpoint in space.(mathematics) a way of making calculations about quantities which are continually changing, such as the speed of a falling stone or the slope of a curved line. Calculus measures little bits of things in order to find out what the whole thing will do. That is the whole theory of calculus. In differential calculus, the changing quantity or variable is measured in an infinitely small amount or size in order for the result of the calculation to be precise.see CALCULUS.