In Latin, jurat means "he swears" (from jurare, to swear). In English, it's a noun. It is the common name for a notary's certificate: the little burst of legalese at the end of an affidavit saying "Sworn to and subscribed before me this ___ day of ___ , etc."
The word is also used generally to refer to any person who has sworn an oath. In the Channel Islands (Jersey, Guernsey, and Alderney) a jurat is a type of magistrate, appointed for life. According to Black's Law Dictionary, juration is the act of swearing. Of course, that's also the way an Englishman says "duration."