open secret
US /ˈoʊpən ˈsiːkrət/
UK /ˈoʊpən ˈsiːkrət/

1.
公开的秘密
a fact that is supposed to be secret but is actually known by many people
:
•
It's an open secret that they are planning to get married.
他们要结婚是公开的秘密。
•
His affair with his assistant was an open secret in the office.
他与助理的恋情在办公室里是公开的秘密。