What is the difference between an autocracy and an oligrachy?

In an autocracy the power to govern is held by one person. The power is inherited or gained by force. Types of autocracy: dictatoship (Hitler, Stalin); absolute monarchy (Louis XIV or Louis XVI; constitutional monarchy(Japan, Britain).

In an oligarchy a small group of people holds the power (eg. China). This group suppresses all political opposition and holds elections but offers just one candidate.