What is truth?

Ever since Pontius Pilate first uttered these words, it is a question which has been haunting mankind, and it is still true today. About 25 years ago I read a book by Ayn Rand and towards the end there is a quote from Aristotle, a great mind. I was so impressed by this and used to know it word by word. But I'm getting on in life and can only now remember.

" For a principle which every one must have, who understands, anything that is. Is not a hypothesis. Evidently then, such a principle, is the most certain of all. Which principle this is, let us proceed to say. It is, that the same attribute, cannot at the same time belong and not belong to the same subject in the same respect."

For some reason this always made immediate sense to me and still does.

So, what is truth?