Most schools of Buddhism explain Nirvana as a state of bliss or peace, and this state may be experienced in life, or it may be entered into at death.
The word Nirvana means "to extinguish," such as extinguishing the flame of a candle. This "extinguishment" is not understood by Buddhists to mean annihilation, however. Rather, it is thought of as passing into another kind of existence.
In the culture in which the historical Buddha lived and taught, it was understood that fire "burns" and becomes visible when it is attached to fuel, and it stops burning and becomes invisible when it is "released" from fuel. The fire, it was thought, was not annihilated but transformed.
In his book Essence of the Heart Sutra, His Holiness the Dalai Lama defined Nirvana as the "state beyond sorrows," or a "state of freedom from cyclic existence."
In Theravada Buddhism, Nirvana (spelled "Nibbana" in Pali) is understood to be an "unbinding" of the mind from defilements, in particular the Three Poisons, and the mental "effluents" of sensuality, views, becoming, and ignorance. It is a liberation from the cycle of death and rebirth and freedom from the effects of karma. In Mahayana Buddhism, Nirvana also is the extinguishing of dualities and a merging with Nirvana and Samsara into an absolute existence.
The various schools of Buddhism have diverse teachings about whether Nirvana can be attained before death or only after death.