I just heard a friend telling me about a concept of gryps. Translating it to English produced very little (let alone anything of relevance).
Originally, a gryps, is a message passed to, from or within a prison. As those messages are likely subjected to discovery and scrutinuous investigation, it's imperative that they can't be broken. Such property can be achieved by pre-deciding a private meaning to a randomly picked and entirely unrelated phrase. For instance: my donkey will eat a banana could be decided among the included parties to mean a shank is under the bed in room 4. It's impossible to trace back the original meaning because there's simply no trace.
Such a concept is also useful for non-prison related communication. What would be a good term for it in English?
I rejected code phrase and pre-assigned sentence as too general. I'd like a more specific and, possibly, less popular term.