The Buddha distinguished the conditioned, which arises, changes and passes away, from the unconditioned, which does not. Nirvāṇa is the unconditioned. A famous passage speaks of an unborn, unbecome, unmade and unconditioned, without which there would be no escape from what is born and made.
Unconditioned
Asaṅkhata: that which is not produced by causes, the early Buddhist description of nirvāṇa.
Also: asankhata