A decentralized autonomous organization (DAO), sometimes called a decentralized autonomous corporation (DAC), is an organization constructed by rules encoded as a computer program that is often transparent, controlled by the organization's members and not influenced by a central government.
There is no CEO, CFO, or anything like that. Every member of the organization has a voice and decides when money is spent from the treasury and on what.
There are eight main types of DAOs:
Protocol DAOs
Grant DAOs
Philanthropy DAOs
Social DAOs
Collector DAOs
Venture DAOs
Media DAOs
SubDAOs
New types of DAOs are being developed regularly, so you may see more types.