Barter is a method of exchange by which goods or services are directly exchanged for other goods or services without using a medium of exchange

Medium of exchange

A medium of exchange is an intermediary used in trade to avoid the inconveniences of a pure barter system.By contrast, as William Stanley Jevons argued, in a barter system there must be a coincidence of wants before two people can trade – one must want exactly what the other has to offer, when and...

, such as money

Money

Money is any object or record that is generally accepted as payment for goods and services and repayment of debts in a given country or socio-economic context. The main functions of money are distinguished as: a medium of exchange; a unit of account; a store of value; and, occasionally in the past,...

. It is usually bilateral, but may be multilateral, and usually exists parallel to monetary systems in most developed countries, though to a very limited extent. Barter usually replaces money as the method of exchange in times of monetary crisis, such as when the currency

Currency

In economics, currency refers to a generally accepted medium of exchange. These are usually the coins and banknotes of a particular government, which comprise the physical aspects of a nation's money supply...

 may be either unstable (e.g., hyperinflation

Hyperinflation

In economics, hyperinflation is inflation that is very high or out of control. While the real values of the specific economic items generally stay the same in terms of relatively stable foreign currencies, in hyperinflationary conditions the general price level within a specific economy increases...

 or deflationary spiral) or simply unavailable for conducting commerce.
Contrary to popular conception, there is no evidence of a society or economy that relied primarily on barter.