This discussion was suggested by JLN and I thought it best to open it with a definition of terms by Kenneth Walker, a once emminent British physician.
<<What is esoteric, or hidden, knowledge? It is a term which has been badly mishandled and which has been used to describe everything from the irresponsible utterances of so-called occult societies to genuine esoteric knowledge. The term should mean immediate, or direct, knowledge, as opposed to mediate, or indirect, knowledge, or knowledge which has been reached through the mediation of the special senses.
Some people repudiate the idea that direct knowledge of this nature exists and maintain that all knowledge must come indirectly through the special senses. Bertrand Russell is one of these, and in his History of Western Philosophy he goes out of his way to point out that there is no method of attaining knowledge other than that used by the scientist. Having had no personal experience of the contemplative method, it is of course natural that he should make this statement.>>
Historically, esoteric philosophy came to the West near the turn of the century with the Theosophy movement. This paved the way for many offshoot movements including those of Rudolph Stiener, G I. Gurdjieff and J. Krishnamurti. It also forms a covert agenda in many popular modern movements such as "The School of Practical Philosophy" e.g.
http://www.practical-philosophy.com/ students of which ( I believe) are asked not to discuss the material outside school.
It would be interesting to hear comments from anyone who has read around, or experienced any of this material