Trade by barter is a system of exchange where goods are directly exchanged for other goods without the use of money. One disadvantage of trade by barter is that the person wishing to buy good X may not have the specific good Y which is what the other party wants. This creates a problem of a double coincidence of wants, which means that both parties must have what the other wants. In this case, the transaction cannot be completed, and trade cannot take place. Hence, trade by barter is not as efficient as using money as a medium of exchange.