What is an economy that lacks a medium of exchange?

An economy that lacks a medium of exchange is typically referred to as a barter economy. In such a system, goods and services are directly exchanged for other goods and services without the use of money. This can lead to inefficiencies, as it requires a double coincidence of wants—both parties must desire what the other has to offer. As a result, barter economies often struggle with trade complexity and limited scalability compared to monetized economies.