Dai is a stablecoin. It is an Ethereum ERC20 token that is pegged to $1 USD — every Dai is worth $1, and will always be worth $1, regardless of how much Dai is in existence. There is no centralized authority like Tether that backs its value, and no traditional bank that backs each Dai with a real US dollar. There is nothing that can be shut down, and no centralized authority that needs to be trusted. Dai lives entirely within the Ethereum blockchain using smart contracts.