noun
A political system where power is held by a small group of people. Often used in historical or political science contexts.
古代ギリシャの一部の都市国家では寡頭政治が行われていた。
Some city-states in ancient Greece were governed by oligarchy.
その国は名目上は民主主義だが、実質的には寡頭政治だ。
That country is nominally a democracy, but in reality it is an oligarchy.