In forex trading, the term “buck” is a slang term for the US dollar (USD). The origins of the term are unclear, but it is believed to have originated in the 1800s, when the skin of a male deer (a buck) was used as a unit of exchange in some parts of the United States. Later, the term “buck” was used to refer to a dollar bill, and eventually to the US dollar as a whole.
The term “buck” is often used in the context of currency pairs that involve the US dollar, such as USD/JPY (US dollar/Japanese yen) or EUR/USD (euro/US dollar). For example, a trader might say that the USD has strengthened against the JPY, meaning that the exchange rate has gone up and it now takes more yen to buy one dollar, or that the EUR has weakened against the USD, meaning that the exchange rate has gone down and it now takes more dollars to buy one euro.