gray area

a grey area {US} AND a grey area {UK} (unclear topic, vague statement; something without a clear rule or answer that is not clearly defined and needs careful judgement) — неясные моменты; область, в которой нет четких представлений; область неопределенных знаний; ~ темные места (контекст.)

Example 1: There are facts that are still in a gray area.
— Остаются факты, в которых еще многое до конца не ясно.
(WM)

Example 2: There are many grey areas in the legal system - many vague laws. (WM)

Example 3: Writing personal email in the office is a grey area that needs to be discussed at the next meeting. (englishclub.com)