In forex, currencies are always traded in pairs. You cannot just buy euros — you buy euros against something else. Usually the US dollar. This is written as EUR/USD. The first currency is the base currency, and the second is the quote currency.
There are seven major pairs, and they account for roughly eighty percent of all forex trading volume. They are:
EUR/USD — Euro vs US Dollar. The most traded pair in the world. It represents the two largest economies on the planet. Tight spreads, deep liquidity, predictable behavior during European and US trading hours.
GBP/USD — British Pound vs US Dollar. Known as "cable" because in the 1800s, the exchange rate was transmitted across the Atlantic via undersea cable. More volatile than EUR/USD, with bigger daily ranges.
USD/JPY — US Dollar vs Japanese Yen. The most active pair during the Asian session. Japan has a unique monetary policy that makes this pair behave differently from the European pairs.
USD/CHF — US Dollar vs Swiss Franc. Switzerland is considered a safe haven, so this pair often moves during times of global uncertainty.
AUD/USD — Australian Dollar vs US Dollar. Heavily influenced by commodity prices, particularly iron ore and gold, because Australia is a major commodity exporter.
USD/CAD — US Dollar vs Canadian Dollar. Closely tied to oil prices because Canada is a major oil producer. When oil rises, the Canadian dollar typically strengthens.
NZD/USD — New Zealand Dollar vs US Dollar. Similar to AUD/USD but smaller and more volatile. Influenced by dairy prices and the Reserve Bank of New Zealand's policies.
Beyond the majors, there are cross pairs — pairs that do not include the US dollar, like EUR/GBP or GBP/JPY. And there are exotic pairs involving emerging market currencies like USD/TRY or EUR/ZAR. These exotics have wider spreads and less liquidity, making them more expensive and riskier to trade.
As a beginner, stick to the major pairs. They have the tightest spreads, the deepest liquidity, and the most predictable behavior. Master one or two pairs before exploring others.