Black market is the phenomenon of buying and selling foreign exchange in the foreign exchange black market.
In countries where it is strictly enforced, it is at the official exchange rate.
Some holders of foreign currency can exchange more of their own currency at a rate higher than the official black market rate, which is the supplier of foreign exchange to the black market.
Other foreign exchange demanders who cannot obtain insufficient foreign exchange at the official rate will purchase it from the black exchange market at a price higher than the official rate.
This is the foreign exchange demander in the black market. The supply and demand of black market foreign exchange constitute the black market exchange rate.