A market economy based on supply and demand with little or no government control. A completely free market is an idealized form of a market economy where buyers and sellers are allowed to transact freely (i.e. buy/sell/trade) based on a mutual agreement on price without state intervention in the form of taxes, subsidies or regulation.
In financial markets, free market stocks are securities that are widely traded and whose prices are not affected by availability.
In foreign-exchange markets, it is a market where exchange rates are not pegged (by government) and thus rise and fall freely though supply and demand for currency.