Blocked Currency
Any currency that is mainly used for domestic transactions and does not freely trade on a forex market (usually due to government restrictions). Also referred to as a "nonconvertible currency".
Investopedia Commentary
It is very difficult (if not impossible) to convert the blocked currency into a freely traded one such as the U.S. dollar.
Related Links
A Primer On The Forex Market
Getting Started In Forex
Floating And Fixed Exchange Rates
See also: Currency, Dirty Float, Floating Exchange Rate, Forex