$BTC The most popular BTC pairs vary depending on the exchange and the time period, but some consistently stand out for their trading volume and liquidity. Based on the provided information and my general knowledge of the market, the most popular BTC pairs usually include:

- BTC/USD: This is undoubtedly the most popular pair. It represents the value of Bitcoin in US dollars, the global reserve currency. Its high liquidity makes it an attractive option for most traders.

- BTC/USDT: Tether (USDT) is a stablecoin, a cryptocurrency whose value is designed to be pegged to the US dollar. The BTC/USDT pair offers a way to trade Bitcoin without the direct volatility of the dollar, making it popular among traders looking to minimize the risk of currency fluctuations.

- BTC/EUR: The Bitcoin/Euro pair is also very popular, especially in Europe and among traders who use the euro as their main currency.

- BTC/ETH: This pair, which trades Bitcoin for Ethereum, is significant because it represents the relationship between the two largest cryptocurrencies by market capitalization. Its popularity reflects interest in both coins and their growth potential.