What is black market please give a real world example under what circumstance do black markets arise?

The black market often sets a price for foreign exchange that is several times the official one. Examples of goods traded in the black market are weapons, illegal drugs, exotic and protected species of animals, and human organs needed for transplant surgeries.

Black markets typically arise when the government attempts to control prices or imposes an excessively high tax burden on transactions. For example, when a government imposes price controls on fuel, individuals willing to pay more than the fixed rate will form the demand side of a black market.

what are the following?

there are many stores that have sales right before christmas