Answer
Not a monomial (because it has more than one term).
Work Step by Step
A monomial is an expression of the form $ax^{k}$,
where $x$ is the variable,
the exponent $k$, a nonnegative integer, is the degree,
and $a$ is the coefficient of the term.
Here, we have a sum of two monomials,
(sum of more than one monomial is a polynomial),
that is, a binomial.
This expression is a binomial,
not a monomial (because it has more than one term).
