(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.
—9th ACC Volume 3 Approved Glossary