only known and understood by a select group of people
esoteric - mysterious
Something ‘esoteric’ is very unusual and typically requires specialist knowledge or interest in order to properly interpret or comprehend it. The word was originally used to express mysterious practices or material designed for a specific group of people regarded as being ‘worthy’ to access it. It can still be used in that context, but is now more commonly seen in relation to something highly technical that is perplexing to a layperson.
The company’s new high-risk investment strategy is quite esoteric. It requires a lot of expertise to properly understand it.
John has a large collection of esoteric books from the Middle Ages dealing with the occult and arcane.
I tried to dip my toe into the esoteric world of molecular science, but it was all too incomprehensible for me.