Strategic ambiguity
In international relations and arms control, strategic ambiguity is a national policy of not confirming or denying the possession of certain military capabilities. It is most common in the context of nuclear weapons, but certainly has been used with respect to other capabilities.
The term is most commonly used regarding Israeli nuclear weapons. It has been used for the U.S. policy of not confirming or denying the presence of nuclear weapons aboard U.S. Navy surface warships, until a declaration was made that they would no longer carry them. South Africa only revealed its nuclear capability after it had voluntarily disarmed.
After the Iraq War, Saddam Hussein appears to have maintained strategic ambiguity about having weapons of mass destruction that Iraq did not actually have, as a means both of deterrence and prestige.