Differential calculus is the study of rates of change of functions using limits and derivatives. The derivative of a function represents the rate of change of the output variable with respect to the input variable or slope at a point. A function is continuous if it has no holes or jumps at any point in its domain. The tangent line approximates the curve at a point, while the normal line is perpendicular to the tangent line. Maxima and minima refer to local extremes where the function reaches a maximum or minimum value. Derivatives can also be used to determine rates of change for a variety of applications.