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

1.
secreto a voces
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.
Es un secreto a voces que planean casarse.
•
His affair with his assistant was an open secret in the office.
Su aventura con su asistente era un secreto a voces en la oficina.