What is Ethereum Dominance (ETHD)?

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