There are many currencies are being traded in this market.
The major pairs are the four most heavily traded currency pairs in the forex market. The four major pairs are the EUR/USD, USD/JPY, GBP/USD, USD/CHF.
These four major pairs are deliverable currencies and are part of the g10 currency group. While these currencies do a significant amount of volume related to economic transactions, these are also some of the most heavily traded pairs for speculative reasons, by traders, as well.
Source: https://www.investopedia.com/terms/forex/m/majors.asp