An analogy to explain a certain (usually political) system, beginning with the statement "you have two cows" and explaining what would happen to them under that system, sometimes involving your neighbours and often the government.
Popularly used for many things, including video games and religions.
Two cows: You have two cows. You use them to explain a political system.
Capitalism: You have two cows. You milk them and sell the milk.
Democracy: You have two cows. You and your neighbours vote on who gets the milk.
Feudalism: You have two cows. The lord tithes most of the milk and lets you keep the rest.
Zork: You have two cows. They get eaten by grues.