What are the requirements for terms to be like terms?

For terms to be like terms, they must have the same variables raised to the same power.

For example, 4x and 3x^2 are not like terms since although they both have x, the x's are raised to different powers. However, 4x^2 and 3x^2 are like terms since they both have only x and for both the x is squared.

They both have to end with a letter like 5x and 9x are like terms