First off I'm not enlightened, and I am not interested in trying to become enlightened unless achieving it meant never being reborn (should the cycle of rebirth exist which I think it likely does, based on observations from masters like Wang LiPing and John Chang)
The most common and excepted definition of enlightenment is a permanent state of non dual awareness (no self/other dichotomy, you and your environment are one entity not separate things)
Everyone has a different idea for it, and no one can agree on one standard definition. Read Mastering The Core Teachings of The Buddha by Daniel Ingram M.D. and see some of the many different models that exist for enlightenment.
I think in the intellectual sense the most common and accepted definition of enlightenment is attaining non-dual awareness which lasts until death.
The mind is conditioned from birth to break apart reality into things and stick labels (words) on them. In reality there are no things, everything is one.
From space you can see a galaxy as one thing, zoom in to a solar system and you can see it as one thing, zoom in on a planet and you can see it as one thing, zoom in and see beings that inhabit it, and see each as one thing, zoom in on their cells, and see each as one thing, zoom in again on their molecules and they appear as one thing, zoom in again on the atoms that make up those molecules and they appear as one thing, zoom in on the subatomic particles, and they appear as one thing, and then their constituents......
Everything we observe appears as something separate from the rest because our minds are conditioned to think that way, and break the whole into chunks. Enlightenment as I understand it de-conditioning your mind to break apart reality into separate things and see everything as a whole including yourself till your death.
I am not sure that is what I am seeking, but I find it fascinating. My primary goal for life is another definition of enlightenment which focuses on ending the cycle of rebirth.
Here are Jed's McKenna's (claims to be enlightened) thoughts on enlightenment:
Interview with Jed McKenna
"I never went in search of spiritual enlightenment. It was never my goal.
I just wanted the truth, whatever the price. I didn't realize until several
years after the successful conclusion of that search that what I had
achieved was called spiritual enlightenment, and even now I don't know
what's so damned spiritual about it." —JED MCKENNA
Q: What is enlightenment?
Q: Okay, what is no-self?
JM: Abiding non-dual awareness.
Q: Okay, what is.......?
JM: I can't tell you what it is; no one can. It's not a thing, it's not a concept,
it's not a place. There's no explaining fire to someone who's never seen fire;
no description can do justice to the direct experience of fire. I use
terms like abiding non-dual awareness and no-self and truth-realization
not because they capture it, but because they seem the least misleading.
Q: Most people define spiritual enlightenment very differently from the
way you describe it, as if they are talking about something completely
different. How can there be such disparity?
JM: Enlightenment is absolute. It doesn't come in varieties or degrees. It's
not open to interpretation. But the most important thing is that it's self-
verifiable and completely available to reason. Anyone who wants to understand
can understand. It doesn't require interpreters or intermediaries. It's
just sitting there, right out in the open, for anyone who cares to look. No
one has to rely on me or anyone else. Becoming enlightened may be a real
ball-buster, but enlightenment theory is a breeze. The first chapter of the
book is titled "That Which cannot be simpler." That's an exact statement.
Enlightenment is that which cannot be simplified further; cannot be further reduced.
Q: Which brings us to the question of Who is enlightened? Who is Writing
the book? Who is teaching? It's very difficult to reconcile the appearance of
self with the claim of no-self.
JM: And yet, there it is. True self is no-self and there's just no Way to make
it sound reasonable. I can't express it in a Way that anyone is going to get
it. I'm aware that there's an apparent contradiction, but it doesn't appear to
me. It's like the gateless gate thing. It looks one Way from there and
another from here. All I can say is come here and see for yourself.
Q: That sounds like a leap of faith, not logic.
JM: No, it's simple math. Anyone can verify for themselves the truth of
non-duality; the fact that all is one. Any reasonably able-minded person
can put it together on their own. From there, it's a short step to no-self.
Once you have established in your own mind the truth of nonduality, then
countless fictions, like the idea of a separate self, shall not long stand.
Q: You say "reasonably able-minded person." What's really required by
Way of intelligence for this undertaking?
JM: Not much. It all really comes back to intent. If the intent is in place,
everything is in place. If the intent isn't in place, no amount of intelligence
will make any difference.
Q: So logic is the tool of the mind and desire is the tool of the heart?
JM: Sure. Good. Logic—mind—is the sword and intent—heart—is the
will to use it. Nicely put.
More of my thoughts on nonduality:
There is no you, there is only the experience OF you.
Every belief, opinion or preference you have ever held or will ever hold, every thought you have had or will ever have, or memory you have ever remembered; has forever and will only ever exist inside of your own mind, and not external to it.
Furthermore everything you've ever seen, heard, smelt, felt, tasted, intuited, remembered, or otherwise experienced has occurred not in some external reality but rather inside your own mind.
When you experience something as occurring external to yourself, what you are witnessing is not an event outside of yourself, it is purely an internal phenomenon.
What I am trying to say in more scientific terms is that bio-electro-chemical messages travel from your sense organs and are sent into your brain, and it interprets these signals and makes sense of them. What is being seen is the interpretation of reality your mind creates, not some objective reality external to you.
Our experience is NOT the thing we observe, but rather more like a painting or a map of the thing our brain is creating a representation of. The reality we experience is purely a mental construct, and itself has no reality external to the mind.
All thoughts, memories, ideas, opinions, verbalizations, vizualizations, have no reality external to the human mind.
All beliefs are maps created by the mind to make sense of reality, however almost all confuse their maps of reality, with reality itself. The map is not the territory, it's a map which represents the territory.
See this painting:
It reads in English: "This is not a pipe" It is not a pipe, it is a painting representing a pipe.
Just as all memories, ideas, concepts, opinions, verbalizations, and visualizations are not reality itself but rather a painting representing reality.
The human ego, personality and identity are self created beliefs, and also have no reality independent of the mind.
So when we burn all our assumptions, beliefs, opinions, paintings, maps and self-made abstract representations of reality to ash, what remains?
Nothing, and no one, forever.
My personal theory is that all that exists is purely information and nothing more, we are all one consciousness experiencing itself subjectively, consciousness is both one whole and infinite. We are like waves moving through an ocean of consciousness, perceiving ourselves as separate while still being a part of the whole.