Nondual awareness is a state of consciousness in which the ordinary sense of separation between observer and observed — between self and world — dissolves. Described across Advaita Vedanta, Dzogchen Tibetan Buddhism, Zen, and Sufi traditions, nonduality points to the recognition that awareness itself — the knowing quality of consciousness — is not a private possession of an individual self but is the nature of experience as such. Sam Harris argues that meditation's deepest benefit is the discovery of this open, spacious quality of awareness that is already present beneath the noise of self-referential thought. Nondual teachings are increasingly being studied in contemplative neuroscience.

Reference:

Wikipedia: Nondualism

https://en.wikipedia.org/wiki/Nondualism