A blocked currency, also known as a non-convertible currency, is the monetary unit of a country where holders of the currency do not have the right to convert it freely at the going exchange rate into any other currency. A currency is considered to be blocked if it fulfills one or more of the following three criteria about usability, exchangeability and market value:
it cannot be used for all purposes without restrictions;
it cannot be exchanged for another currency without limitations;
It cannot be exchanged at a given exchange rate.