What's the difference between an emperor and a king?

An Emperor has an empire that includes Kingdoms which the Emperor rules over.

An emperor reigns over an empire, a geographically extensive group of states and peoples. An emperor can also be a king or queen regnant, as were George V, VI, and Victoria of Great Britain, who were emperors of India.

"An empire is a state with politico-military dominion of populations who are culturally and ethnically distinct from the imperial (ruling) ethnic group and its culture..." http://en.wikipedia.org/wiki/Empire

A king or queen regnant reigns over a smaller territory, a kingdom.

An emperor has more lands and more people and is higher in ranking than a King and Queen Regnant, but equal to a King-Emperor, Queen-Empress.

An emperor is of an empire which consists of more than one country, while a king is of one country only.

That's the theory, anyway. In practice, it's never that simple. The British Empire never had an emperor, except for Queen Victoria styling herself Empress of India, and that continued until India became independent. The story is that as her eldest daughter Vicky married the Emperor of Germany, she didn't like being outranked by her own daughter.

The only emperor in the world today is the Emperor of Japan, but the Japanese empire consists only of Japan, so he ought to be a king. Go figure!

A King is the ruler of a Kingdom. An Emperor is ruler of a vast territory. There were usually not many emperors, perhaps 3 or 4 (Roman Emperor, Byzantine [east roman] Emperor, Holy Roman Emperor were the most common). you have a much higher status than a king but still you are probably related to all the kings in europe

...an Emperor can be (self proclaimed) A King is from a Royal Order...a line of historic progression.

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