An affidavit is a testimony of facts in written form, signed in front of a court-approved authority. Affidavit definition: .See examples of AFFIDAVIT used in a sentence. The affidavit and claim you have just received means you are being sued in the small claims division of the district court. They have a terrible title, and they are full of legalese. Allegation — A declaration, assertion, or statement of a party to a lawsuit, made in a pleading, and setting out what the party intends to prove. An affidavit is a legal document that takes the place of oral testimony in legal proceedings. 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. These legal documents are used in conjunction with witness statements or related evidence in a dispute.