An open secret is a concept or idea that is "officially" secret or restricted in knowledge, but is actually widely known; or refers to something which is widely known to be true, but which none of the people most intimately concerned are willing to categorically acknowledge in public.
Famous quotes containing the words open and/or secret:
“A man’s most open actions have a secret side to them.”
—Joseph Conrad (1857–1924)
“His mind of man, a secret makes
I meet him with a start
He carries a circumference
In which I have no part.”
—Emily Dickinson (1830–1886)