poly = many, non-polynomial would be a monomial (one). so an example of a polynomial, f(x) = x^3 + 2x + 1 monomial: f(x) = 2x (only one term!)
Polynomials have non-negative integer exponents. This means that the exponents on the variable are 0, 1, 2, 3, etc. If you have something like x^(3/2), it is not a polynomial.