Early Chinese translators tried some forty Chinese words before finally giving up and simply transliterating this Sanskrit word, which means absence of breath. It's also defined as the only calm. Most people equate it with death, but to Buddhists nirvana means the absence of the dialectic that breath represents.
According to Nagarjuna, "That which is, when subject to karma, samsara, is, when no longer subject to karma, nirvana."
---Red Pine, in the notes of his translation of The Zen Teachings of Bodhidharma---