An unknown known is information that an individual or organization has in its possession but whose existence, relevance or value has not been realized.
An unknown known could be, for example, knowledge that a single person at a company possesses. Because the employer lacks that information, there is a risk that it will be lost if that individual retires or otherwise leaves the business.
“The Unknown Known” is also the title of Errol Morris’ 2013 documentary about Donald Rumsfeld. The title comes from the former Secretary of Defense’s statement at a 2002 United States Department of Defense briefing:
“As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don’t know we don’t know.”