DAI is a stablecoin created by MakerDAO project, pegged to US Dollars (meaning 1 DAI = 1 USD) to prevent price volatility and built on top of the Ethereum network. As opposed to other stablecoins like Tether (where USDT is created by the company itself with no “tangible proof” of equivalent USD existent - there is no public audit), DAI offers complete transparency because the tokens are backed by Ether, which in turn are locked into smart contracts, publicly available on the blockchain. This means everyone can check the existence of these locked coins. DAI’s stable price is guaranteed by a series of mechanisms that prevent the coin to go above or below 1 USD.
For more technical information about DAI stablecoin, please visit the official MakerDAO website
Thanks to Eidoo Wallet, it's possible to gain interests on deposits by swapping DAI with cDAI tokens: in this article we illustrate how to do it.