Keeping in mind our previous definition of a monomial, a polynomial is simply the sum of a finite series of monomials. 2x^2 + 15x - 4xy^4z^2 is an example of a polynomial. It is the sum of a finite series of monomials, namely, three nomials. Keep in mind that a single term can itself be a polynomial. For a term to be a polynomial, it does not have to be more than one term, counterintuitive though that may sound. For example, -40z^9 is a polynomial. We produce this by adding a finite number of monomials together. When the sum of monomials do not have like terms, and are therefore not reducible to a single term, they constitute a polynomial. Indeed, we use the familiar concept of the "term," introduced before, to refer to the individual constituents of a polynomial.