I'm thinking of things like general relativity or the Dow Jones Industrial Average. You have a general idea about what context the name belongs to but probably don't understand it well enough to explain what it is to someone else. Is there a word or phrase to express that?
Jargon -- ODO
noun 1. Special words or expressions used by a profession or group that are difficult for others to understand.
Example: legal jargon, medical jargon
You should consider rocket science.
[mass noun, usually with negative]
Something very difficult to understand.
‘we want you to get out and vote—it's not exactly rocket science’
known or knowable only to a few people
I consider this a better answer than jargon, which is terminology peculiar to a field. General relativity does have jargon such as gravitational lensing but it is the concepts that are difficult rather than the words that express them.