What makes two terms "like terms"

Give an example of two or more like terms:​

3x^3 + 8x + 9x + 3x^2 + 1 + 4x^3 + 3 + 2x^2

Like terms in this -

3x^3, 4x^3
3x^2, 2x^2
9x, 8x
3, 1

I think you get the gist.
Basically you can add them if they have the same value/degree

The answer is 1 because you have to flip the sign when dividing by negative number and 3