For me, this is a topic that has been broached many times.
I have been asked to do this before.
But even after continuous revisitation, it is still a difficult issue to contain in one general definition.
People are so different.
So far, the best I can do is this:
Intelligence is the propensity to doubt.
Intelligence lies not in the number of answers accumulated during one's lifetime, but rather in one's ability to ask the right questions.