Answer:
Monarchy- a form of government in which the people are led by one ruler, usually a king, who takes power legally and often hands the throne down to his son.
Oligarchy- a form of government in which the people are led by a small group of people, often wealthy aristocrats. This isn't usually very beneficial to the majority of the population.
Tyranny- a form of government very similar to monarchy, except a tyrant doesn't take power legally and can claim no right to the throne. A tyrant usually doesn't pass power to his son, and despite common stereotypes, not all tyrants were bad leaders.
Democracy- a form of government led by the people, either through representatives or directly. Democracy in ancient Athens was a direct democracy, in the USA today we have a representative democracy.