OLIGARCHY –
The rule of the few over the many(word has Greek origin) is a form of power structure in which power effectively rests with a small segment of society.

PLUTOCRACY-
Plutocracy is rule by the wealthy, or power provided by wealth. The combination of both plutocracy and oligarchy is called plutarchy (word also has Greek origin).

DEMOCRACY-
Is a political form of government in which governing power is derived from the people.