Nibbana is an existing reality, an article by Bhikkhu Bodhi
Regarding the nature of Nibbana, the question is often asked: Does Nibbana signify only extinction of the defilements and liberation from samsara or does it signify some reality existing in itself? Nibbana is not only the destruction of defilements and the end of samsara but a reality transcendent to the entire world of mundane experience, a reality transcendent to all the realms of phenomenal existence.
The Buddha refers to Nibbana as a 'dhamma'. For example, he says "of all dhammas, conditioned or unconditioned, the most excellent dhamma, the supreme dhamma is, Nibbana". 'Dhamma' signifies actual realities, the existing realities as opposed to conceptual things. Dhammas are of two types, conditioned and unconditioned. A conditioned dhamma is an actuality which has come into being through causes or conditions, something which arises through the workings of various conditions. The conditioned dhammas are the five aggregates: material form, feeling, perception, mental formations and consciousness. The conditioned dhammas, do not remain static. They go through a ceaseless process of becoming. They arise, undergo transformation and fall away due to its conditionality.
However, the unconditioned dhamma is not produced by causes and conditions. It has the opposite characteristics from the conditioned: it has no arising, no falling away and it undergoes no transformation. Nevertheless, it is an actuality, and the Buddha refers to Nibbana as an unconditioned Dhamma.
The Buddha also refers to Nibbana as an 'ayatana'. This means realm, plane or sphere. It is a sphere where there is nothing at all that correspond to our mundane experience, and therefore it has to be described by way of negations as the negation of all the limited and determinate qualities of conditioned things.
The Buddha also refers to Nibbana as a, 'Dhatu' an element, the 'deathless element'. He compares the element of Nibbana to an ocean. He says that just as the great ocean remains at the same level no matter how much water pours into it from the rivers, without increase or decrease, so the Nibbana element remains the same, no matter whether many or few people attain Nibbana.
He also speaks of Nibbana as something that can be experienced by the body, an experience that is so vivid, so powerful, that it can be described as "touching the deathless element with one's own body."
The Buddha also refers to Nibbana as a 'state' ('pada') as 'amatapada' - the deathless state - or accutapada, the imperishable state.
Another word used by the Buddha to refer to Nibbana is 'Sacca', which means 'truth', an existing reality. This refers to Nibbana as the truth, a reality that the Noble ones have known through direct experience.
So all these terms, considered as a whole, clearly establish that Nibbana is an actual reality and not the mere destruction of defilements or the cessation of existence. Nibbana is unconditioned, without any origination and is timeless.