Knowledge?

Ignoring Gettier (justification thought experiment) problems, knowledge is best defined as "justified true belief".

In the Apology, Plato relates that Socrates accounts for his seeming wiser than any other person because he does not imagine that he knows what he does not know.

ἔοικα γοῦν τούτου γε σμικρῷ τινι αὐτῷ τούτῳ σοφώτερος εἶναι, ὅτι ἃ μὴ οἶδα οὐδὲ οἴομαι εἰδέναι.

I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either.