Advaita
अद्वैत (advaita)
Non-dualism - the teaching that ultimate reality is not divided into separate selves and separate divine.
Advaita, literally not-two, names a school of Vedantic philosophy holding that the apparent multiplicity of separate selves and a separate divine reality is, at the deepest level of analysis, not ultimately real - that atman and brahman are, in essence, identical rather than distinct.
This is a claim with real consequences for practice. If the sense of a separate self is, as advaita argues, a layer of misperception rather than a final fact, then spiritual practice is reoriented away from acquiring something new and toward recognizing something that was never actually absent.
Advaita is one philosophical position among several serious ones within the broader tradition, not a settled consensus, and traditions that disagree with it, favoring various forms of qualified or unqualified dualism, do so with equally serious textual and experiential arguments of their own.