Bitcoin dominanceis bitcoin's marketcap dividend by the marketcaps of all cryptocurrencies combined. It shows how much value bitcoin has versus the all cryptos combined. This is important because it shows the relative strength of altcoins over time. For most of bitcoin's lifetime (pre-2017), dominance sat at over 98%. Bitcoin was the entire market. But since the first altcoin boom in 2017, it has never come close to that peak again..