The document defines and provides examples of different types of functions:
1. Constant functions where f(x) = a for all values of x (e.g. f(x) = 2).
2. Linear functions of the form f(x) = ax + b (e.g. f(x) = 5x+3).
3. Quadratic functions of the form f(x) = ax2 + bx + c (e.g. f(x) = 3x2 + 2x + 1).