"There is that dimension where there is neither earth, nor water, nor fire, nor wind; neither dimension of the infinitude of space, nor dimension of the infinitude of consciousness, nor dimension of nothingness, nor dimension of neither perception nor non-perception; neither this world, nor the next world, nor sun, nor moon. And there, I say, there is neither coming, nor going, nor staying; neither passing away nor arising: unestablished, unevolving, without support (mental object). This, just this, is the end of suffering."  
Udana VIII.1

Literally: the extinction of fire, the ceasing of fever, calming of the wind.

An all-inclusive definition of this technical term is impossible.
 

Not belonging to the range of temporal/spatial existence, the understanding of nirvana (absolute knowledge, perfect wisdom, experience of totality, prajña-paramita) goes beyond the cognitive capabilities of samsaric beings, attached to their ego-delusion.
 

Unlike the samsaric cycle of suffering in which everything is linked to everything, nirvana could be called an “absolute unbound state of freedom”.

Nirvana can only be approached gradually.
 

In human dualistic thought there are two ways of approach, both equally relative. There is however a certain difference qua tension.