The prefix "eso", from the Greek, means "within". But... this simple reference to the term "within" refers to subtle realms of vibrational energy that cannot be perceived using one's brain and physical senses. And, the term "esoteric" was created to "stand for" [or to refer specifically to] these subtle non-tangible, non-physical realms of energy that are normally hidden from human experience.
QUESTION: 
Can these subtle, non-tangible realms be discovered?
This is THE question, isn't it? And how one answers this question is more important than hardly anyone realizes. Unfortunately the psychologically SAFE answer is "no" they cannot be "defined or studied" [this is what B.F. Skinner believed... fortunately he was wrong]. The actual and honest answer is "yes" they can be Known... but not by ones brain or by thinking... they can be Known by using the rarely discussed faculty of "Intuition"....and this moves us well beyond what is ordinarily discussed in modern mental health, or in education for that matter.
If you clicked on "Intuition" above, then you know about Intuition and something of the reason it is so rarely considered as a viable tool that any reasonable person should make use of... and yet, few people do so. The reason is explained in "Intuition". So we won't duplicate all that here.
The point being made here is that the Esoteric realms existing within you and that cannot be accessed by your brain, or by reading about them...are available to you via your own Intuition. But since this faculty seems come on its own, how does one use it... this is explained in "Intuition".. so take some time, unless you already have, to read it. Your MIND realm is a fascinating study that one could spend a lifetime discovering... and I have done just that. You can study your fascinating MIND [at least abstractly] by clicking HERE . Rare are those of us who have been able to retain access to the faculty of intuition... despite education unintentionally working to eliminate it from within us. The "natural" thing for someone who is stuck in the Left-Hemisphere of his/her brain to do is to remain so busy "thinking" that he/she never notices his/her intuition. The field of education does its best to reinforce this ceaseless thinking and focusing outside oneself from grammar school through graduate school.
The reason "thinking" is seemingly natural is that "thinking" is a major way in which ones MIND prevents one from from being exposed to the "Unknown" deeply repressed within ones MIND realm. Indeed, fixing ones Attn Aspect of Apapsyche in ones L-H of ones brain and feeding thoughts to the L-H is a primary Defense Mechanism of ones MIND. The MIND uses what I call Delusional Thinking [which are thoughts fed to the L-H of ones brain expressly to direct ones thinking in a certain way and for a specific defensive and self-protective purpose... which remains fully non-conscious to the one being directed]. When some deeply repressed trauma stored deep within ones MIND is vibrationally stimulated, and the natural reaction of the Attn Aspect of ones Apapsyche would be to quickly withdraw into ones MIND realm, ones MIND anticipates this event and redirects ones Attn Aspect of Apapsyche into ones L-H by feeding Delusional Thinking into the L-H which forces ones Attn Aspect of Apapsyche to remain in ones L-H "thinking" about the thoughts needing to be thought about.
Unfortunately, the field of mental health is quite ignorant regarding this basic Defense Mechanism of the MIND. In addition, after a century of "modern mental health" denying and ignoring the MIND and Spiritual realms within Man, there are very few left in mental health who have any idea what the MIND is, or how it works within Man. The brain is unable to perceive the subtle energy of the MIND, and thus, when it receives Delusional Thinking from the MIND, ones brain simply assumes that such thoughts are coming from itself and it follows these thoughts precisely. The concept of ones brain being "directed" by ones MIND would not set well with people, of course... if this fact could ever reach their conscious awareness without being cut off at the pass by their MINDs feeding them thoughts that convince them that what is happening could not happen.
The single most difficult roadblock facing people in need of what EsoEducation has to offer them are the tens of thousands of mental health professionals who have been trained to deny and ignore the MIND, who have no idea what the MIND is, and would not believe that their MINDs will busily feed Delusional Thinking to their brains causing them to "see" EsoEducation as a threat and something to try and destroy.
What is the answer? To emphasize the fact that EsoEducation is purely an educational activity, and it has nothing at all to do with psychology, counseling, or mental health as currently structured. For an explanation of Apapsyche, try this.