Well, “black market” is trade in illegal things. In the USSR, the “black market” included food and clothing. In North Korea, the black market includes books and information.
In the US the black market is substantially drugs, guns, and prostitution.
As for “black economy”, maybe the asker means “underground economy”, which is anything traded that is not reported to the government.
So the entire “black market” is part of the underground economy, along with most children’s lemonade stands, some restaurant and delivery tips, and other things that are done on a cash basis.
That is why governments are so hot to go “cashless”, because then every transaction is tracked, and taxed, and there cannot be any “underground economy”.
