Calculus is an advanced branch of mathematics that deals mostly with rates of change. More generally, calculus (plural calculi) refers to any method or system of calculation guided by the symbolic manipulation of expressions.
There are two main branches of calculus: differential calculus and Integral calculus. Differential calculus concerns rates of change and slopes of curves. Integral calculus concerns accumulation of quantities and the areas under and between curves.
Examples of other well-known calculi include propositional calculus, calculus of variations, lambda calculus, and process calculus.
vCalc's Calculus library contains equations in differential and Integral calculus.