In Forex market the currency expressed as the cross-rate. In this configuration, the two currencies are listed in an XXX/YYY ratio, with the XXX position referred to as the base currency. The base currency is usually expressed as a whole number, while the YYY position is expressed as the decimal that most closely matches the based currency rate.
The smallest fraction, or decimal, in which a currency can be traded, is called a pip and this is usually the degree to which a cross-rate is expressed. For example, if the British pound sterling can be traded in thousandths, the currency will be expressed to the third decimal place. The U.S. dollar is often expressed to the hundredth of a cent.