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:
“Why make so much of fragmentary blue
In here and there a bird, or butterfly,
Or flower, or wearing-stone, or open eye,
When heaven presents in sheets the solid hue?”
—Robert Frost (1874–1963)
“The secret of being a bore is to tell everything.”
—Voltaire [François Marie Arouet] (1694–1778)