I a looking for a legal term, probably in Latin, they I seem to recall being mentioned in the last year or two here. I am keeping it deliberately vague; I am not seeking legal advice, only the name of the legal term. It goes something like this.
1.) Joe Citizen goes to an official (usual govt., could be any kind of official) seeking guidance on the proper course of action for a desired result.
2.) The Official, who *should *know the answer, gives Joe guidance.
3.) Joe, acting in good faith and as a reasonable person would, acts on said guidance.
4.) It is subsequently revealed that the Official Guidance is wrong.
5.) Officialdom informs Joe he can’t do what he did, and Joe will not receive the result he hoped for.
6.) Joe seeks a remedy based on Latin Legal Term I Can’t Recall.
There’s no Latin term for it. Estoppel is a civil doctrine (and not a Latin term). In US federal criminal law it would usually be described as reasonable reliance on an official interpretation (or pronouncement) of the law. In Canadian law, it’s called officially induced error [of law].
The Latin term you are thinking of may be ignorantia juris non excusat (idomatically, “ignorance of the law is not an excuse”), which official reliance is - sometimes - an exception to. Or perhaps mens rea - the mistake of law defense is used to establish that a defendant did not have the state of mind required to meet the crime charged.
Note too that as to a civil claim or defense, it is very difficult to successfully establish estoppel against the government. The law is very reluctant to bind the government to erroneous interpretations of the law by its employees.
Reliance to detriment sounds a lot like “reliance based estoppel” according to the Wiki article. The key elements I suppose are:
So it seems to me they key in the OP’s question is “The Official, who should know the answer, gives Joe guidance”. How knowledgeable is the official and to what extent was the advice given as mere guidance, or unconditional fact?
In case it’s specifically a Latin phrase you want to use, the closest equivalent to the concept of estoppel in legalese Latin would be venire contra factum proprium, which translates as going against one’s own action.