esoteric
adj.adj. understood by only a small number of people who have special knowledge or interest. You might describe a joke, a hobby, or a book this way if most people find it confusing.
adj. intended for or likely to be understood by only a small number of people with specialised knowledge or interest. Frequently applied to obscure academic fields, niche hobbies, or mystical traditions.
The professor's lecture on ancient poetry was too esoteric for most students.
He collects esoteric jazz records from the 1960s that only a handful of dedicated musicians have ever heard of.
The software manual was filled with such esoteric jargon that even seasoned programmers struggled to configure the system without consulting external forums.
Learned borrowing from Ancient Greek ἐσωτερικός (esōterikós, “belonging to an inner circle”), from ἐσωτέρω (esōtérō, “further inside”), comparative of ἔσω (ésō, “within”), from ἐς (es), εἰς (eis, “into”) (the term esoteric referred originally to the secret teachings of Greek philosophers, versus public or exoteric ones).
The adjective can be used attributively or predicatively. It frequently collocates with nouns denoting information, such as 'knowledge', 'jargon', 'details', or 'subjects'.