I'm always on the hunt for easy to understand definitions of nonduality to share with people who have never contemplated the concept before. Mostly I tend to use Jerry Katz's FAQ pages on What Is Nonduality, with my favourites being this one, this one, and this one. I wonder if the wikipedia entry for nonduality could be updated somewhat to include some of that content. Jerry, if you're reading this right now, what are your thoughts on that? Indeed, have you already contributed to that wiki entry?
From Ken Wilber's A Brief History of Everything, the following definition resonates pretty strongly with me:
Across the board, the sense of being any sort of Seer or Witness or Self vanishes altogether. You don't look at the sky, you are the sky. You can taste the sky. It's not out there. As Zen would say, you can drink the Pacific Ocean in a single gulp, you can swallow the Kosmos whole--precisely because awareness is no longer split into a seeing subject in here and a seen object out there. There is just pure seeing. Consciousness and its display are not-two.That's the kicker for me, right there: Consciousness and its display are not-two.
(x-posted to

I really like the "not-two" description.