adjective /ˌɛs.əʊˈtɛɹ.ɪk,ˌɛs.əˈtɛɹ.ɪk,ˌɛs.oʊˈtɛɹ.ɪk/
a) Understood only by a chosen few or an enlightened inner circle.
The writing in this manual is very esoteric; I need a degree in engineering just to understand it!
b) Having to do with concepts that are highly theoretical and without obvious practical application.
Wikipedia foundation.