Easiest way to understand DAOs are with examples:
Bitcoin can be considered to be the first true DAO, It provides an operating system for money without banks and bank managers, which anybody is free to adopt, and has stayed attack resistant and fault-tolerant since the first block was created in 2009. However, Bitcoin lacks governance rules that are characteristic of DAOs.
Ethereum With the emergence of the Ethereum Network, the concept of DAOs moved up from blockchain protocol to the smart contract. Smart contracts are necessary ingredients for DAOs to be possible. Nonetheless, Ethereum itself is not a DAO but a framework for developing DAO projects.