Rank refers to the position of a cryptocurrency by market cap, volume, TVL etc.
For example, Bitcoin ($BTC) is the leading cryptocurrency as it has the largest market cap out of every cryptocurrency, therefore $BTC ranks number 1. Depending on the statistics you are searching for, different cryptocurrencies will hold different rankings. These rankings can be discovered across many price-tracking websites such as CoinMarketCap and CoinGecko for example.
