A black market was a market in which all applicable taxes and/or regulations were avoided.[source needed] Items could be bought on the black market by those not legally able to purchase them otherwise, often for a substantial fee.
There was a black market selling alien species on Earth in the 21st century. John Harrison paid millions for a group of Skullion slaves who had crash landed in Central Asia. They were brought across Europe and then across the English Channel. (TV: The Man Who Never Was)
Bloorm Vungah Bart Slitheen, Dax Fex Fize Slitheen and Korst Gogg Thek Lutiven-Day Slitheen were planning to sell Luke Smith's telekinetic energy on the Energies Black Market on Antara IV, but couldn't fulfil their plans because Luke escaped. (PROSE: The Lost Boy)