Spread: The spread is the difference between a currency pair's bid and ask price. For the most popular currency pairs, the spread is often low - sometimes even less than a pip! For pairs that aren't traded as frequently, the spread tends to be much higher. Before a Forex trade becomes profitable, the value of the currency pair must cross the spread.
At the end of 1913, nearly half of the world's foreign exchange was conducted using the pound sterling.[24] The number of foreign banks operating within the boundaries of London increased from 3 in 1860, to 71 in 1913. In 1902, there were just two London foreign exchange brokers.[25] At the start of the 20th century, trades in currencies was most active in Paris, New York City and Berlin; Britain remained largely uninvolved until 1914. Between 1919 and 1922, the number of foreign exchange brokers in London increased to 17; and in 1924, there were 40 firms operating for the purposes of exchange.[26]

Imagine a trader who expects interest rates to rise in the U.S. compared to Australia while the exchange rate between the two currencies (AUD/USD) is .71 (it takes $.71 USD to buy $1.00 AUD). The trader believes higher interest rates in the U.S. will increase demand for USD, and therefore the AUD/USD exchange rate will fall because it will require fewer, stronger USD to buy an AUD.
Volatility is what keeps your trading activity moving. However, if you're not careful it can also completely destroy it. When volatile, the market moves sideways, which makes spreads grow and your orders slip. As a beginner Forex trader, you need to accept that once you are in the market, anything can potentially happen, and it can completely negate your strategy.
The foreign exchange market is unique for several reasons, mainly because of its size. Trading volume in the forex market is generally very large. As an example, trading in foreign exchange markets averaged $5.1 trillion per day in April 2016, according to the Bank for International Settlements, which is owned by 60 central banks and is used to work in monetary and financial responsibility. 
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