Definition
The base currency is the first currency in a quoted pair and represents the unit whose value is being expressed in the quote currency.
In market context
In EUR/USD, EUR is the base currency and the quoted number states how many U.S. dollars correspond to one euro. Buying the pair generally means taking a long position in the base currency relative to the quote currency; selling means the reverse exposure. Account currency, settlement rules, lot size, and conversion costs can affect the cash result even when the pair’s price move is understood correctly.
Source
Use the primary source for fuller regulatory or market context.
