It is dangerously facile to talk about ‘The Absence of Subject’ to one firmly ensconced in it. It is markedly unwise to try and explain the phrase: ‘The Absence of the Separated Self’ to one who can only interpret the explanation from the platform of a presumed ‘Self’.
The answer to the question: ‘What is Nirvāṇa?’ lies in an understanding of the misunderstanding that underlies the question itself.
The self-scuttling has to be done at the level of the questioner. And to properly sunder the Self-Loop is to comprehensively answer the question.
Nirvāṇa in its proper definition has nothing at all to do with any empyrean ecstasy, cosmic peace or any of that later rubbish. And no, upon reaching it you still will not be able to part the Red Sea.
The word Nirvāṇa long predates the Buddhist literature. And the problem of ambitious Guru’s unknown to Shūnyam who pin a plethora of enticing and outright misleading attributes on Nirvāṇa is a very old one.
The word Nirvāṇa, literally a ‘Flaring-Out’, has its etymological roots in a fire that has ‘Come to Rest’. The original verse [MadhimaNikaya] says it is like asking the direction taken by a dead fire. To ask: ‘In which direction has [the dead] fire gone?’, is a question that: ‘does not fit the case’.
In the common analogy, its like explaining life outside water to a fish that has known nothing else and cannot conceive it with any credence.
The fish is an easier case. With us humans, explanation is both unconvincing and deleterious. We refuse to understand that we cannot understand; what we conventionally mean by ‘Understanding’ itself begins in the Separation.
It’s sort of like the situation at the counter at the Rolls-Royce dealership. If you need to ask the price you probably can’t afford it. If you need to have Nirvāṇa explained, you won’t understand it.
The Diamond Sūtra uses Nirvāṇa and Tat-āgatha alternatively and synonymously. I don’t actively use them because they have accumulated so much dust and debris over the millennia that it would take several Posts just to get them cleaned up over a hot bath.
But if you want Nirvāṇa converted to a Self-Eating Expression, into the language of this Site, it would be as: ‘The Exhaustion of Philosophical Views’ [Is that a view?]
‘There is not a whit of difference between Nirvāṇa and Saṃsāra’, the Buddhist Scholar-Monk Nagarjuna [100 C.E.] famously declared. And in case you find that ambiguous or unconvincing, he adds: ‘And there is not a whit of difference between Saṃsāra and Nirvāṇa’.
Nagarjuna was a teacher. And he had to take a stand while others had the luxury of deflecting questions. Allowing for that, the proper declaration is: ‘Nothing at all may be said about Nirvāṇa from the stance of Saṃsāra. Not that they are the same; not even that they are ‘Not-Different”.