Calculus

Calculus is the mathematical study of change. It provides two major techniques: Differential calculus and integral calculus, which are, in a way, the opposite of each other.
Differential calculus, to find the rate of change of a given function
Integral calculus, to find a function to a given rate of change

Both techniques are based on the fundamental term limit of function.
The idea of a limit separates calculus from disciplines like algebra, geometry or trigonometry, which are useful to describe static situations.