Oligarchy is a form of power structure
Power structure
Power Structure may refer to:* Hierarchy* The Establishment...

 in which power
Political power
Political power is a type of power held by a group in a society which allows administration of some or all of public resources, including labour, and wealth. There are many ways to obtain possession of such power. At the nation-state level political legitimacy for political power is held by the...

 effectively rests with an elite class distinguished by royalty, wealth, family ties, commercial, and/or military legitimacy. The word oligarchy is derived from the Greek words "ὀλίγος" (olígos), "a few" and the verb "ἄρχω" (archo), "to rule, to govern, to command".

Throughout history, most oligarchies have been tyrannical
A tyrant was originally one who illegally seized and controlled a governmental power in a polis. Tyrants were a group of individuals who took over many Greek poleis during the uprising of the middle classes in the sixth and seventh centuries BC, ousting the aristocratic governments.Plato and...

, relying on public servitude
Servitude may refer to:* Service* Conscription* Employment* Slavery* Indentured servitude* Involuntary servitude* Penal servitude* Servitude * Equitable servitude, a term of real estate law* Servitude in civil law...

 to exist, although others have been relatively benign.