An affidavit is a written statement. A person, known as the affiant, swears under oath to the statement's truthfulness.Affidavit. An affidavit is a sworn statement, subject to penalty or perjury, which generally is made out of court. Affidavit. An affidavit is a sworn statement to the court subject to the penalty of perjury. Typically, affidavits are made out of court. An affidavit is a written statement made under oath that is typically used in legal proceedings. Learn their purpose, when to use, and how to write. Affidavit evidence of publication. An affidavit of service is a legal receipt which confirms the delivery of documents from one party to another party in legal matters. The taking and recording of testimony of a witness under oath before a court reporter in a place away from the courtroom before trial.