Leverage simply means borrowing money needed to make a trade, and in Forex terms, this money is borrowed from the broker. This is one huge advantage of the Forex market, whereby brokers allow you to trade up to 2% of the overall contract size (50:1) compared to stock market (2:1). You can use the small account to trade large sizes where wins can be quite large and you only need a small capital to obtain it.
The need to exchange currencies is the primary reason why the forex market is the largest, most liquid financial market in the world. It dwarfs other markets in size, even the stock market, with an average traded value of around U.S. $2,000 billion per day. (The total volume changes all the time, but as of August 2012, the Bank for International Settlements (BIS) reported that the forex market traded in excess of U.S. $4.9 trillion per day.)