Calculus is a branch of mathematics that deals with finding derivatives and integrals of functions. It was originally developed in the 17th century by Newton and Leibniz and is used in many fields today including economics, engineering, biology, astronomy, and more. Some examples of how calculus is used include modeling orbital mechanics for space probes, determining credit card interest rates, and calculating bacterial growth rates when variables are altered. In summary, calculus plays a crucial role across many sectors in exploring the world, developing technology, and driving innovation.