In Buddhism, nirvana is the final state the soul reaches on its journey through different lifetimes. These lifetimes are pictured as a series of lamps, one being lit by another, until the final lamp goes out. The word "nirvana" means "going out" or "extinguishing."
According to Buddhists, our desires and cravings are what keep the process of reincarnation going. By eliminating all desires it is possible to escape the cycle of rebirth. When a person manages to extinguish all his desires, he reaches a state of nirvana and is said to be a saint.
When a saint dies he enters nirvana proper, in which he loses his identity as a distinct individual. Buddha compared the question "Does a saint survive his death?" to the question "Where does a flame go when it is blown out?" Both questions are thought to be intrinsically unanswerable. Neither a dead saint nor a blown-out flame have individual identities anymore.
Nirvana is different from the Christian idea of heaven. Nirvana is a state of desirelessness; heaven is a state of having one's most fundamental desire (for God) fulfilled. Nirvana is a state of ultimate apathy and indifference, heaven of ultimate joy and fulfillment. Paradoxically, Buddhists regard nirvana, the state of desirelessness, as the most desirable state.
Nirvana also differs from heaven because it suggests one will eternally lose his body and his individual identity, while Christians claim they will keep both of them eternally.