The probable meaning of Nirvana
In Pali Buddhist scripture, the word Nibbana (Sanskrit: nirvana) always appears in context, never as a clear definition (and which would have produced closure). For instance,
“Calming of all conditioned things, giving up of all defilements, extinction of ‘thirst’, detachment, cessation, Nibbana.”
“O Bhikkhus, whatever there may be things conditioned or unconditioned (this is nonsense, my insertion), among them detachment is the highest. That is to say, freedom from conceit, destruction of thirst, the uprooting of attachment, the cutting off of continuity, the extinction of thirst, detachment, cessation, Nibbana.”
“The cessation of continuity and becoming is Nibbana.”
Whether or not Nibbana sums up (or abstracts) the context elements or is wholly different from them has remained a fruitful mystery to this day.
What the Buddha seems to be saying is that the elimination (i.e. stopping) of striving (i.e. of becoming), and of its drivers (for instance, greed, hatred and delusion), ends as Nibbana. In short, Nibbana ensues when striving (for life) comes to rest. Ergo,
Nibbana (Nirvana) = @ rest