Tutoring English, vocabulary is always interesting. The tutor mentions esoteric.
Esoteric (adj) means not meant for public consumption, and refers to knowledge. Usually something esoteric is secret because even if untrained people do encounter it, they can’t understand it. However, esoteric information may be “classified” anyway, in case a few people not meant to know it manage to decipher it. Technological secrets can be thought of as esoteric.
Mish, Frederick C. (editor). The Merriam-Webster Dictionary. Springfield: Merriam-Webster, 2004.Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.