A country's exchange rate regime where its currency is set by the foreign-exchange market through supply and demand for that particular currency relative to other currencies. Thus, floating exchange rates change freely and are determined by trading in the forex market. This is in contrast to a "fixed exchange rate" regime.
In some instances, if a currency value moves in any one direction at a rapid and sustained rate, central banks intervene by buying and selling its own currency reserves (i.e. Federal Reserve in the U.S.) in the foreign-exchange market in order to stabilize the local currency. However, central banks are reluctant to intervene, unless absolutely necessary, in a floating regime.
In the modern world, most of the world's currencies are floating, such currencies include the most widely traded currencies: the United States dollar, the euro, the Norwegian krone, the Japanese yen, the British pound, and the Australian dollar. The Swiss franc was formerly traded via a floating exchange rate but as of September 2011, has its floor pegged to the euro. However, central banks often participate in the markets to attempt to influence the value of floating exchange rates. The Canadian dollar most closely resembles a "pure" floating currency, because the Canadian central bank has not interfered with its price since it officially stopped doing so in 1998. The US dollar runs a close second, with very little change in its foreign reserves, in contrast, Japan and the UK intervene to a greater extent.