Currency pairs
Currency pairs are combinations of two currencies. In the EUR/USD combination, for example, the euro is the base currency and the US dollar the quote currency. The 7 most traded currencies are called the ‘majors’
Major currencies;
The 7 major currencies and their percentages are listed below. As each transaction involves 2 currencies, the total trading can be considered to be 200%. The USD makes up 85% of this trade volume. The EUR/USD is by far the most traded currency pair, followed by the USD/JPY, GBP/USD and USD/CHF.

Currency crosses
Currency cross pairs are currency pairs that do not involve the USD. Back in the old days, if someone wanted to change currencies, they would first have to convert their currencies into USD, and only then could they convert their dollars into the currency they desired. With the invention of currency crosses, traders can now bypass this process and trade currencies directly against each other. Examples are GBP/JPY, EUR/JPY, EUR/CHF, and EUR/GBP.
Exotic currency pairs
Exotic currency pairs are currency pairs whereof one currency from an emerging economy is traded against the USD or EUR. Examples are the EUR/TRY (euro vs. the Turkish lira) and the USD/MXN (U.S. dollar vs. the Mexican peso).
Trading in exotic currency pairs does have some disadvantages. The spread is usually much wider and, because they are traded less frequently, liquidity is much lower and they may show large movements quite unexpectedly.