In forex market the currency pair is the quotation of the relative value of one currency unit against the another currency. The currency that is used as the reference is called the counter currency or the quote currency and the currency that is quoted in relation is called the base currency.
Currency pairs are written by concatenating the ISO currency cods of the base currency and the counter currency, separating them with a slash character. A widely traded currency pair is Euro currency against the US dollar, coded as EUR/USD.
The most traded currency pairs in the world are called the “Majors”. They involve the currencies Euro, US dollar, Japanese Yen, Pound sterling, Australian dollar, Swiss dollar and Canadian dollar. The price of one currency constantly changes the another.
The price of EUR/USD pair shows how much EUR you can buy for 1USD. The first currency in the pair is a base currency and the second currency is quote currency. In the trading market the major currency pairs can perform nearly 75 percent, these are EUR/USD, GBP/USD, USD/CHF and USD/JPY. In all the above examples US currency is along with many currencies, hence US dollar is the major currency pair.