Definite integral is an integral with upper and lower limits. Let f be a continuous function on the closed interval [b, a]. The definite integral of f from b to a is defined to be the limit $\int_{b}^{a}$ where "a" is known as upper limit and "b" is known as the lower limit. $\int_{b}^{a}f(x)\ dx = F(a) - F(b)$.