An affidavit is a written statement that you swear is true and that may be used as evidence in a court of law. Both copies will be required in court.An affidavit translation is a formal statement sworn under oath. It can also refer to a sworn translation of an official document like a marriage certificate. A written statement that someone makes after promising officially to tell the truth. An affidavit can be used as proof in a law court. Word History and Origins​​ Origin of affidavit1. A declaration in writing made upon oath before a person authorized to administer oaths, esp for use as evidence in court. Find definitions for specific words, phrases, and terminology used in the Massachusetts Court System.