The Foreign Exchange market (also referred to as the FX or Forex market) is the largest financial market in the world, with over $1.5 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.