What is enlightenment?

Following his awakening the Buddha encountered a wandering ascetic. The ascetic asked Buddha who his guru was and what spiritual training he followed. Buddha responded that he was the "Victor and Conqueror of the World, superior to gods and men, an Enlightened One without teacher or precedent". The ascetic looked carefully, but saw nothing in Buddha's appearance or nature to indicate that he spoke the truth. So he sighed and passed on, saying "If only it were so".

The ability to play the piano does not mean the player understands music.  It just means that she no longer needs to learn the names of the keys.  So too with awakening or "enlightenment".  Just because you or anyone else has a deep intense experience which results in profound life changes, does not mean awakening has occurred. It just means some ignorance has been removed, some unneeded habits let go. The removal of ignorance is not awakening.

Sitting under the Bodhi tree Buddha stopped looking for diversions. He stopped looking for improvement. He stopped looking. He realized that all searching was pointless, and just relaxed under the tree for the rest of his life. He no longer needed to be diverted from this moment. But although "living in the moment" is quite nice, it is too pat an answer. Living in the moment is not awakening. It is just discipline. Similarly the "all is one" or "non-dual" or "permanent bliss" perspectives seem formulaic, and somehow lacking.  Isn't real awakening more basic?

Perhaps enlightenment is simply the  absolute and permanent absence of a subject to any object.

Simple, easy, and no big deal