FOREX (FOReign EXchange market), refers to an international exchange market where currencies are bought and sold. The Foreign Exchange Market that we see today began in the 1970's, when free exchange rates and floating currencies were introduced. In such an environment only participants in the market determine the price of one currency against another, based upon supply and demand for that currency.
FOREX is a somewhat unique market for a number of reasons. Firstly, it is one of the few markets in which it can be said with very few qualifications that it is free of external controls and that it cannot be manipulated. It is also the largest liquid financial market, with trade reaching between 1 and 1.5 trillion US dollars a day.