Differential calculus, Branch of mathematical analysis, devised by Isaac Newton and G.W. Leibniz, and concerned with the problem of finding the rate of change of a function with respect to the variable on which it depends. Thus it involves calculating derivatives and using them to solve problems involving non constant rates of change. Typical applications include finding maximum and minimum values of functions in order to solve practical problems in optimization.

Source: https://www.britannica.com/science/differential-calculus

Differential Calculus is the branch of mathematics that studies the rate of change of quantities. The means to mathematically cut something into small pieces to find how it changes.