From The Art and Popular Culture Encyclopedia
Nondualism (also non-duality) is a term and concept found in mysticism, metaphysics, psychology and philosophy. Within psychology and mysticism it refers to states of consciousness in which there is no distinction between the subject's sense of a self and the contents of the subject's awareness (the objects of consciousness). Within Yoga this is technically called absorption (dhyana). Nondualism also refers to a theological doctrine derived from the Upanisads which posits that the original essence of the human soul is indistinguishable from and thus identical with the Absolute or Godhead, Brahman. This is contrasted with the view that there is a perennial distinction between the soul and the divinity. Nondualism is sometimes conflated with Monism.
"Nondualism", "nonduality" and "nondual" are terms that have entered the English language from literal English renderings of "advaita" (Sanskrit: not-dual) subsequent to the first wave of English translations of the Upanishads commencing with the work of Müller (1823–1900), in the monumental Sacred Books of the East (1879), who rendered "advaita" as "Monism" under influence of the then prevailing discourse of English translations of the Classical Tradition of the Ancient Greeks such as Thales (624 BCE–c.546 BCE) and Heraclitus (c.535 BCE–c.475 BCE). The first usage of the terms are yet to be attested. The English term "nondual" was also informed by early translations of the Upanishads in Western languages other than English from 1775. The term "nondualism" and the term "advaita" from which it originates are polyvalent terms. The English word's origin is the Latin duo meaning "two" prefixed with "non-" meaning "not".