The document defines the derivative of a function as the limit of the average rate of change of the function over an interval as the interval approaches zero. It provides examples of calculating the derivative of various functions, including the velocity and acceleration of the function s(t)=t^3 - 2t^2. The derivative of s(t) is 3t^2 - 4t, the velocity is 3t^2 - 4t, and the acceleration is 6t - 4. Formulas are provided for taking the derivative of various functions.