Made up for a Base currency and a Quote currency (or Counter currency), it’s the way of displaying and pricing one currency against another to be used to make a trade. Currency pairs are normally shown as two abbreviated currency names, separated by a slash. The slash can sometimes be omitted, showing only the two currency abbreviations, side-by-side.
The most traded currency pairs in the world are called the Majors. They include the currencies euro, US dollar, pound sterling, Canadian dollar, Swiss franc, Japanese yen, and Australian dollar. The Majors make up the largest share of the foreign exchange market and exhibit high market liquidity.