USDD is a stablecoin issued by the TRON DAO Reserve, pegged to the US dollar. It offers a decentralized cryptocurrency for blockchain transactions and can be used for payments, trading, staking, and as a value store. To ensure stability, USDD is backed by cryptocurrencies like Bitcoin, Ethereum, and TRON, and the reserve is over-collateralized, holding more assets than the amount of USDD in circulation.