The Sanskrit word samsara means "journeying." In Buddhism, as well as in Hinduism and Jainism, samsara is defined as a cycle of birth, death, and rebirth.
Samsara is sometimes thought of as a circumstance or an illusion. In Buddhism it is also thought of as the process by which karma causes rebirth.
Samsara is sometimes depicted as the opposite of Nirvana. However, the Mahayana school of Buddhism views both Nirvana and Samsara as mental representations. To one who appreciates the true nature of the world, Nirvana and Samsara are not different from one another.