Nirvana is a religious term associated with Asian religions. From a Sanskrit word for “to blow out,” nirvana is the state of being free from suffering: the fires of desire have been blown out.
In Buddhism, the goal is to achieve enlightenment—the realization that what we think of as our permanent, existing self is an illusion. Nirvana is the final stage of enlightenment. When the state of nirvana is achieved, all entanglement and attachment to life has ceased and one is free from the effects of karma* and the cycle of death and rebirth.
In Hinduism and Jainism, nirvana is the liberation of the soul from the effects of karma and bodily existence that makes union with the Absolute possible.
In non-religious English use, nirvana has come to mean a state of oblivion or perfect happiness.
*karma: the sum of a person’s actions in one of his successive states of existence, regarded as determining his fate in the next; hence, necessary fate or destiny, following as effect from cause.