unwritten law

详细解释:不成文法
【经】 不成文法, 习惯法, 普通法

英语解释：

名词 unwritten law:

law based on customary behavior

例句：

It's an unwritten law around here that everyone fetches his own coffee, even the managers.这儿有一条不成文法，即每人自己去取咖啡，哪怕是经理也是如此。