grey area 灰色地带，中间区域(界线不明、不易归类、难以界定或处理的领域或形势)

【例句】
Many banks have already spun off prop desks, which would clearly fall foul of the new rules, but a vast grey area of activity remains.
许多银行已经拆分了显然会与新规冲突的自营交易部门，但这些交易活动仍在大量的灰色地带存在。

Exactly what can be called an offensive weapon is still a grey area.
究竟什么可称作进攻性武器仍然难以界定。