Any currency that is used primarily for domestic transactions and is not openly traded on a forex market. This usually is a result of government restrictions, which prevent it from being exchanged for foreign currencies. Also known as a "blocked currency". 

|||As the name implies, it is virtually impossible to convert a nonconvertible currency into other legal tender, except in limited amounts on the black market. When a nation's currency is nonconvertible it tends to limit the country's participation in international trade as well as distort its balance of trade.