A currency pair or else an exchange rate is a quotation of two different currencies (i.e. EURUSD). The first listed currency of a currency pair (i.e. EUR) is called the base currency, and the second currency is called the quote currency (i.e. USD).
■ There are 8 major currencies: United States Dollar (USD), Euro (EUR), Japanese Yen (JPY), United Kingdom Pound (GBP), Switzerland Franc (CHF), Canadian Dollar (CAD), Australian Dollar (AUD), and New Zealand Dollar (NZD)
■ The are also 7 major currency pairs that are called the 'Majors' and include the US Dollar against EUR, JPY, GBP, CHF, CAD, AUD, and NZD.
These are some of the most tradable Forex currency pairs.