Forex Market is any place where currencies of different countries are bought or sold. The complete term is Foreign Exchange Trading and the term forex is only an abbreviation of the complete term. Unlike the NYSE or any other stock exchange there in not a single centrally cleared marketplace where this exchange is conducted but a set of interconnected market places. The main trading centers for these are located in London, Singapore, New York and Tokyo. In the world of global business many transactions are conducted. To complete these transactions payments need to be made in a certain currency.
This creates demand for a certain currency (using which the said payment has to be made) and this currency has to be purchased, or exchanged, using another currency. This demand and supply equation causes the exchange rate fluctuations. The reasons for change are discussed later in detail. Around ten years ago only large banks and institutions participated in forex trading. This was because only these could muster the requisite tools and systems needed to participate in this complex trading. But this scenario was soon changed by advent of certain technologies which have enabled even retail investors to participate in these markets.

Other details

The forex market is the largest and the least regulated market in the world. It also has the distinction of being open for all times of the day and night, except weekends. This is because when the Asian segment closes, the European segment opens and when the European one closes the American segment opens. The cycle is completed when on the closure of the American segment the Asian one opens. The volume of trade and the liquidity in the market is unparalleled and so is the geographical dispersion of the market.