In the forex market, there is a bid price and an ask price. The difference between the two is called the spread. Bird Watching in Lion Country by Dr Forex talks about how the bid is the price at which buyers are willing to buy, and the ask is the price at which sellers are willing to sell. There are four known currency pairs that dominate the majority of trades. These four currency pairs are known as the Euro and U.S. Dollar, the U.S. Dollar and the Japanese Yen, the U.S. Dollar and Swiss Franc, and the U.S. Dollar and the British Pound.