A DAO, or a Decentralized Autonomous Organization, is a company set up to run by code on the blockchain. DAOs are new generation of decentralized organizations based on blockchain. The people who own tokens associated with the DAO are responsible for voting on changes and proposing new ideas to keep the DAO up and running and improving.
If you want to know fundamental of blockchain, check this:
DAO is based on smart contracts, you can know more about smart contracts in this video:
DeFi solutions are demonstrated in DAO and make it possible, you can find here:
https://www.youtube.com/watch?v=OQQ99HX06zw