Polynomials are algebraic expressions consisting of variables, constants, and exponents combined using operations like addition, subtraction, multiplication, and division. They are classified based on the number of terms as monomials, binomials, or trinomials. The degree of a polynomial refers to the highest exponent present. Common polynomial operations include adding and subtracting like terms, multiplying polynomials according to distributive properties, and using long division to divide polynomials. Division of polynomials does not always result in another polynomial.