‘What is nonduality? In this Mahayana Buddhist setting, it is a vision of reality that derives from the “emptiness” of all things, the truth that nothing exists in and of itself, that things are always in the process of change, and that this change occurs through their fundamental dependence on other impermanent things. Nothing is ever completely separate from other things, and nothing remains the same over time; hence the duality of division between things is ultimately an illusion. From this point of view, reality as it is bequeathed to us through our culture’s common sense is an illusion, a dream from which we must awaken if we are to see the truth. This new truth, however, is not simply a new set of beliefs. On the contrary, it transcends the very conceptual form that the old truths once assumed. It is not graspable, not something that can or must be believed. It is not an assertion about how things really are, because “all assertions can be refuted and confounded.”‘
That’s it in a nutshell.