The document discusses the Fundamental Theorem of Calculus, which states that differentiation and integration are inverse operations. It explains that the theorem connects the two major branches of calculus - differential and integral calculus. The theorem also shows that the net change in an accumulation function F(x) over an interval [a,b] is equal to the definite integral of F'(x) from a to b. In other words, it connects the integral and derivative of a function.