What is a currency pair?
It is a currency against another currency, forex currencies are available in pairs, you cannot sell or only buy one currency, you must buy or sell a currency in another currency and this is the reason behind trading in Forex in pairs.
Example:
The currency of the European euro against the currency of the US dollar, in the language of traders these two currencies are called "the euro-dollar pair" and the symbol for this pair is EUR / USD
Second: Forex Types and Pairs:
Major Currencies
Minor Currencies
Cross pairs (crosses)
Exotic Pairs