Explanation:

Barter is an alternative method of trading where goods and services are exchanged directly for one another without using money as an intermediary. ... While uncommon, barter still does occur on the margins in some markets such as the business-to-business (B2B) space and some consumer services.
In its simplest form, bartering is the exchange of one valuable product for another between two individuals. Person A has two chickens but wants to get some apples; meanwhile, Person B has a bushel of apples but wants some chickens. If the two can find each other, Person A might trade one of his chickens for a half-bushel of Person B's apples. No medium of exchange is used.
The problem posed by simple bartering is what economists call the "double coincidence of wants." In this case, Person A is not satisfied unless he crosses paths with a chicken-wanting apple-carrier, while Person B needs an apple-wanting chicken-carrier.