Korean yen
The Korean yen was the currency of Korea between 1910 and 1945. It was equivalent to the Japanese yen and consisted of Japanese currency and banknotes issued specifically for Korea. The yen was subdivided into 100 sen. It replaced the Korean won at par and was replaced by the South Korean won and the North Korean won at par.
Convertibility
Some countries pass laws restricting the legal exchange rates of their currencies or requiring permits to exchange more than a certain amount. Some currencies, such as the North Korean won, the Transnistrian ruble, and the Cuban national peso, are officially nonconvertible and can only be exchanged on the black market. If an official exchange rate is set, its value on the black market is often lower.