Vivarta is the Advaita account of causation, by which the effect is an appearance of the cause without any real change in it, as a rope appears as a snake. Brahman appears as the world without becoming it. It is contrasted with pariṇāma, real transformation, as milk really becomes curd, the view of Sāṃkhya and of some Vedānta schools.
Vivarta
Apparent transformation: the Advaita view that the world is an appearance of Brahman, which does not itself change.
Also: Vivartavada