What is Bitcoin Dominance (BTCD)?

Bitcoin dominance (BTCD) is a metric that measures the market cap of bitcoin (BTC) — the world's largest cryptocurrency — in relation to the total market cap of all other cryptocurrencies combined. BTCD is often perceived to have a correlation to the performance of Ethereum and all other alternative cryptocurrencies, or altcoins. Generally, when BTCD decreases, the value of other cryptocurrencies increase in what is sometimes referred to as an "alt season." However, when BTCD increases, BTC tends to outpace other cryptocurrencies.