Polynomials are algebraic expressions with whole number exponents. A polynomial can be classified based on the number of terms as a monomial, binomial, trinomial, or multinomial. It can also be classified based on degree, which is the highest sum of exponents of variables in any term. Polynomials can be added or subtracted by combining like terms, where like terms have the same variables and exponents. Unlike terms are kept separate when adding or subtracting polynomials.