A market economy, also widely known as a "free market economy," is one in which goods are bought and sold and prices are determined by the free market, with a minimum of external government control.
A market economy is the basis of the capitalist system. The opposite of a market economy — i.e, a "non-market" or "planned" economy — is one that is heavily regulated or controlled by the government, most notably in socialist or communist countries. Feelings run high among supporters of both types, as exemplified by the famous American economist Milton Friedman who said that "Underlying most arguments against the free market is a lack of belief in freedom itself." Ouch.