Saṃsāra is a Sanskrit word that means "wandering" or "world", with the connotation of cyclic, circuitous change. It also refers to the theory of rebirth and "cyclicality of all life, matter, existence", a fundamental assumption of all Indian religions. Saṃsāra is sometimes referred to with terms or phrases such as transmigration, karmic cycle, reincarnation, and "cycle of aimless drifting, wandering or mundane existence".

The concept of Saṃsāra
 has roots in the Vedic literature, but the theory is not discussed there. It appears in developed form, but without mechanistic details, in the early Upanishads. The full exposition of the Saṃsāra doctrine is found in Sramanic religions such as Buddhism and Jainism, as well as the various schools of Hindu philosophy, after about the mid 1st millennium BCE.