A corporation is an artificial legal entity given the legal rights of a real person. Corporations are typically made up of a hierarchically organized group of people. A corporations primary goal and function is to generate large, growing, sustainable legal returns for its shareholders with no regard for its stakeholders such as its employees or customers.
Corporations are the dominant institutions of or time. Many multinational corporations have more revenue than small governments.
The 2003 documentary "The Corporation" does an excellent job explaining what a corporation is and its impact modern society. It points out that corporations are "legal persons" with all the characteristics of a psychopath.