Samsara (meaning an endless cycle of reincarnation and suffering) is central to Hinduism's doctrine of metempsychosis. According to this belief, human spirits or souls (jivas) are bound by action (karma), creating an endless cycle of birth and death with each new life depending on one's actions being judged for merit by merit of action (karma). At death, their spirit or soul (jiva) are transmigrated into another body depending on previous karma such as being human, animal or plant. Human existence seeks liberation by reaching Nirvana or reaching Nirvana through self-realisation through attainment of liberation from this cycle by reaching Nirvana or attaining Nirvana.
Buddhism takes an alternative view on reincarnation called Samsara. Contrary to Hinduism's doctrine of an eternal soul, which asserts its existence through belief in an immortal soul, Buddhist cosmology believes reincarnation can occur via six realms - humans, animals, hellish beings (hell), heavenlies and hungry ghosts; demigod or asura beings may also reincarnate in Samsara if their previous lives left bad karma that causes their souls to enter it reincarnations; demigod or asura realms can even happen if their past lives had such bad karma from previous lives that caused them to come back through.
Liberation from Samsara can be achieved through loving devotion (bhakti) in dualistic Hindu traditions and meditation (dhyana) in nondualistic traditions; yet many remain stuck in Samsara for their entire lives, unable to escape its bonds due to past karmas.