Base currency refers to the primary currency against which other currencies or assets are measured or traded. In the case of cryptocurrency exchanges, the base currency is typically the one in which the trading pair is quoted. For example, if you see a trading pair like BTC/USD, Bitcoin (BTC) is the base currency, and the US Dollar (USD) is the quoted currency.

This means that the price of Bitcoin is expressed in terms of US Dollars. Traders use the base currency to evaluate the value of other cryptocurrencies. When trading, they can easily understand how much of the base currency is required to buy or sell an asset.

The choice of base currency can impact trading strategies, liquidity, and market dynamics. Popular base currencies include Bitcoin, Ethereum, and stablecoins like USDT, as they provide a reference point for many trading activities. Understanding which currency serves as the base can help traders make informed decisions.