An emperor is a (male) monarch, usually the sovereign ruler of an empire or another type of imperial realm. Empress, the female equivalent, may indicate an emperor's wife (empress consort), mother (empress dowager), or a woman who rules in her own right (empress regnant). Emperors are generally recognized to be of a higher honor and rank than kings, and are generally the highest temporal political rank/honor in existence. The term itself is of Old French origin and was derived from "Imperator" which was the title of the Roman head of state during the Roman Republic and, post-Augustus Caesar, the Roman Empire, and itself roughly means "commander."
See Special:Whatlinkshere/Etymology:Emperor for a list of articles using this term.