A currency pair is the quotation of the relative value of a currency unit against the unit of another currency in the foreign exchange market.
Currency pairs are generally written by concatenating the ISO currency codes (ISO 4217) of the base currency and the counter currency, and then separating the two codes with a slash. Alternatively the slash may be omitted, or replaced by either a dot or a dash. A widely traded currency pair is the relation of the euro against the US dollar, designated 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, Canadian dollar, and the Swiss franc.