The Foreign Exchange market (also referred to as the Forex or FX market) is the largest financial market in the world, with over $5 trillion changing hands every day.
That is larger than all US equity and Treasury markets combined!
Unlike other financial markets that operate at a centralized location (i.e. stock exchange), the worldwide Forex market has no central location. It is a global electronic network of banks, financial institutions and individual traders, all involved in the buying and selling of national currencies. Another major feature of the Forex market is that it operates 24 hours a day, corresponding to the opening and closing of financial centers in countries all across the world, starting each day in Sydney, then Tokyo, London and New York. At any time, in any location, there are buyers and sellers, making the Forex market the most liquid market in the world.