A function describes the relationship between variables where a change in one variable causes a change in the other. The independent variable is called the domain and the dependent variable is called the range. Functions can be explicit, where the dependent variable is directly defined in terms of the independent variable, or implicit, where the variables are mixed in the relationship. Functions can also be increasing or decreasing based on whether the dependent variable increases or decreases as the independent variable increases. Other types of functions include even functions, where f(-x)=f(x), odd functions where f(-x)=-f(x), and polynomial functions defined by a polynomial equation.