A DAO, or a decentralized organization, as defined by Vitalik Buterin - founder of Ethereum, is "a virtual entity that has a certain set of members that [...] have the right to" spend the entity's funds and modify its code". The aim of such an organization is to replicate "the legal trappings of a traditional company or nonprofit but using only cryptographic blockchain technology for enforcement."
A DAO can be used to create any virtual entity. Some possible examples are a fully automated company, a fully automated decision apparatus, a crowd-funding platform, a ride-sharing platform, etc. Therefore, a DAO is not a particular type of business model, or a certain type of organization, but rather a concept that can be used to represent a large variety of things.
From a legal perspective, one of the main debates is whether a DAO should be recognized as a legal person (to which extent a DAO can be perceived as a separate legal entity from its human actors), which directly determines to which extent those actors can be protected from the liabilities of the DAO. However, the common understanding at the moment is that it can not be considered an entity segregated from the human actors that operate it (i.e: as a legal person). That is because the legal personhood can only be established proven there are one or more identified actors responsible for the actions of a particular entity, which is in contrast to the "autonomous" nature of the DAO.
For a better understanding of a DAO, read the following article: Decentralized Autonomous Organization; S. Hassan and P. De Filippi (https://policyreview.info/glossary/DAO)
https://www.waceo.org/ —legal for DAOs
Some popular DAOs and platforms that allow you to create your own DAO (some even without coding them yourself):