"Classify the polynomial by the number of terms" means a term contains both the variables and its coefficient. For example a "monomial" has one term like [tex]2x^{2}[/tex].
A binomial has 2 terms like [tex]3x^{2}+6x[/tex]
A trinomial has 3 terms like [tex]4x^{2}+5x-8[/tex]
And a polynomial has 4 or more terms.
So basically one can classify the type of polynomial by counting the number of terms in a given equation.