It's a term described as the 8th and final limb of mental "yoga" [union with divinity]
It describes how inner and outer states of being are experienced and understood as one. Seth describes how a persons inner mental state produces their outer world/experience.
It's one of my favorite terms because there isn't a commonly known English equivalent except maybe the term "dissolution" used in certain contexts.
https://en.wikipedia.org/wiki/Samadhi#Etymology
Sanskrit[edit]
Various interpretations for the term's etymology are possible:
sam, "together"; a, "toward"; stem of dadhati, "puts, places": "a putting or joining together;"[web 2]
sam, "together" or "integrated"; ā, "towards"; dhā, "to get, to hold": "to acquire integration or wholeness, or truth" (samāpatti);
sam, "uniformly" or "fully"; adhi, "to get established: : a state wherein one establishes himself to the fullest extent in the Supreme consciousness;
samā, "even"; dhi, "intellect": a state of total equilibrium of a detached intellect.
sam, "perfect," "complete." dhi, "consciousness": a state of being where "all distinctions between the person who is the subjective meditator, the act of meditation and the object of meditation merge into oneness."
sama, "equanimous" dhi,"buddhi or the intellect"[7]