A polynomial containing two unlike terms is called a binomial.

Do you know what unlike terms are? If not, you can find simple examples of unlike terms in the article Like terms.

Binomial example:

2a + 5b

There are only two terms in this polynomial. That is why it is a binomial.

Binomials examples:

123abd +5

456x^{2}y^{3}z^{4} - 2xy

456x

These polynomials (each consisting of only two terms) are binomials.

Note, this is not a binomial:

2x + 5x

Why is it not a binomial? It is not a binomial because it consists of two like terms. We can add like terms:

2x + 5x = 7x

The 7x is a monomial and not a binomial.

So the sum of two like terms is not a binomial.