This exotic sounding word has a surplus of subtle variations, though all closely related to each other. First off, it can describe something (tangible or intangible) that is rare or of special interest. It can also be used to mean confidential or private, or at least limited to a limited group of individuals. Lastly, it can describe that which is only understood by or designed for a small group of people, or even that which is just plain difficult to understand by most. Very mysterious, no”
Example: When the three old friends got together every few years, they quickly reverted back to their cocky days of graduate studies in design where they were continually striving to one-up each other with some newly found (or, occasionally, fabricated) esoteric design theory.