Final answer:
A trinomial is a polynomial with three terms. The expression x + y - 13 is a trinomial because it has three terms: x, y, and -13.
Step-by-step explanation:
A trinomial is a polynomial with three terms. In the given expression, x + y - 13 is a trinomial because it has three terms: x, y, and -13. The term 4xyz is not a trinomial because it has only one term.