Definition: A polynomial equation with two terms usually joined by a plus or minus sign is called a binomial. Binomials are used in algebra. Polynomials with one term will be called a monomial and could look like 7x. A polynomial with two terms is called a binomial, it could look like 3x + 9. It is easy to remember binomials as bi means 2 and a binomial will have 2 terms.
3x + 4 is an example of a binomial. A binomial is a polynomial.