What is nirvana? - An explanation of enlightenment and nirvana in plain English
In order to understand what or where is nirvana, it is necessary to understand what is meant by "being enlightened" or "gaining enlightenment" in Buddhism. Unfortunately, there has not been many teachers of Buddhism that can explained these concepts clearly. At least in all my years learning Buddhism, I have only met one person who has explain it in a clear way to me. Perhaps it is my bad karma not to have met any good teachers.
"Enlightenment" and "nirvana" has always been explained away with non-explanation such as "it cannot be described, and can only be realized" etc. As such, many Buddhists themselves has no clear understanding of what "being enlightened" is. Many think that attaining a high level of concentration during meditation (aka attaining the jhanas/dhyana) is enlightenment. Worse, some "so-called" Buddhists actually think that having supernatural powers is enlightenment.
In Buddhism, being enlightened is to realize the reality of "no-self". This is the minimium level of realization one needs in order to escape the cycle of death and rebirth, in order to be recognized as "enlightened". A person who has thoroughly realize this principle is also known as a arhat.
What is this principle of "no-self"? Since I'm not an enlightened person (otherwise I'll be an arhat already!), I will just explain this as best as I can intellectually understand it. This is a disclaimer that I may be wrong, so don't just take my word for it.
To put it simply, the principle of "no-self" states that the concept of the self or "me" is basically an illusion. [Or as the Diamond Sutra puts it,"the arhat no concept of me, human, living being, sentient being."(Chinese text)]. If you live your life centered around your "self", you will never find true happiness. On the contrary, if you take the "self" for real, you will find suffering in life, and rebirth after you die.
So, what is this "self" that is an illusion? The "no-self" here refers not so much to "no you, no me" as some Buddhists like to put it, but more of the "self" as in selfless and selfish. "No-self" is closer in meaning to "being selfless" rather than "no you, no me". Do not confuse "no-self" with "no identity"!
Well, you may ask,"If everyone gives up the concept of self, won't we all become one uniform mass of identity-less clones walking around? Isn't that a bleary, boring and scary place?" No, as mentioned earlier, do not confuse "no-self" with "no identity". The latter is the result of denying the self rather than realizing no-self. [On the contrary, the Buddha assures us, on realizing the "no-self" principle, we will become a truly happy person.]
Any proof, you ask? Consider these ancedotal evidences of the truth of "no-self": - All "selfish" happiness, ie those based on gratifying the "self" are impermanent. They will come to an end eventually. The longest known last a human lifespan. Not many last even that long. (In Buddhism, happiness that are not permanent are not considered true happiness)
Altruism and selfless actions are considered as virtue in all races, cultures and religions.
Selfless persons are in general happier and more at peace than selfish persons.
A person who has realized "no-self" ie an enlightenment person, has the following character:
All his actions are borned out of altruism. Totally kind and sincere.
He never gets angry when insulted or hurt. No hatred at all, not even towards his enemies and evil people.
He is totally humble.
Peaceful, serene. Not affected by bad, as well as good incidents
Cannot be hurt internally
(You can use these yardsticks to measure any self-proclaimed enlightened person. Just try to provoke his anger by insulting him)
This is attainable. We have read about and probably met these type of people, to various degrees, both Buddhist and non-Buddhist. Enlightenment is not an exclusive right of Buddhist alone.
Now back to nirvana. To understand what or where is nirvana, it is useful to think of it from both the point of view of the unenlightened observer, and that of the observed (the enlightened person).
To the unenlightened observer who cannot fathom the idea of "no-self', everyone must either go "somewhere" after death or disappear into "nothingness". To them, nirvana is "something" an enlightened person "enters" when he/she passes away. "State" would probably be the best term for that "Something". Because to say it is a place is not correct because you can't find it, and you can't point to a direction or describe where it is. To say that it is "nothingness" is also not correct because an enlightened person, if he choose to, can take a "self" and be reborn into the world again in order to help teach unenlightened beings.
Well, if that sounds confusing, the tricky part is still ahead. To the enlightened person, there is really nothing that "enters nirvana" because having realized "no-self", there is no "self" that can go into nirvana! To put it another way, if there is no "self" that can be reborn, what "self" is there to enter nirvana? So, the term "nirvana" is really quite irrelevant as far as the enlightened person is concerned!
If all these doesn't make sense to you, don't worry. I'm just explaining on a intellectual level, and my intellect may not make sense to you or anyone. The best way to find out is to go find out and understand for yourself!