When there are three terms, it's a trinomial:

So, what about four terms?  Quadnomial?  Naw, we don't go there.  Too hard to pronounce.

This guy is just called a polynomial:

There's one more word I need to tell you about:

degree

Here's how you find the degree of a polynomial:

Look at each of the terms...
Whoever has the most letters wins!

Check it out:

This is a 5th degree polynomial:

This guy has 5 letters...
The degree is 5.