the.com/esotericism

means The practice of cultivating hidden, specialized knowledge meant to be grasped only by a select few who've earned or been initiated into it.

from Rooted in the Greek 'esoterikos,' meaning 'inner,' from 'esotero' ('more within' or 'further inside') — the comparative form of 'eso,' meaning 'within.' It was reportedly used by ancient Greek philosophers, including those in Aristotle's circle, to distinguish teachings reserved for inner-circle students from the 'exoteric' lessons given to the general public. The word carried that velvet-rope spirit of inner-sanctum knowledge into modern usage, where it came to describe any body of understanding deliberately kept esoteric — that is, within — rather than shared freely.