"Is there any different between an Emperor and a King? Or they are actually the same, and it is just a matter of terminology?" asks a student in Tom's short story class, while we are talking "The Emperor's New Clothes."
I thought it is a terminology matter, but I am wrong! According to Wikipedia, an emperor is a (male) monarch, usually the sovereign ruler of an empire or another type of imperial realm, while king is a (male) monarch, or head of state. Emperors are generally recognized to be above kings in honor and rank. Empress and queen are the feminine forms of emperor and king respectively.
However, Czar, Tzar, and Tsar are the titles of former emperor of Russia. Kaiser is refered to German and Austrian emperors.