these four walls字面意思是“这四面围墙”，其实在口语中是用于叮嘱保守秘密，即“打住，到此为止”。

【例句】
I don't want to repeat anything，these four walls.
我不想重复任何事情，到此为止。

Don't let this go further than these four walls.
走出这屋就不要再谈这事了