An affidavit is a sworn statement of fact that can be used in a variety of legal proceedings, from bankruptcy cases to family and civil litigation matters. A written declaration upon oath made before an authorized official.An affidavit is a sworn written statement that can be used in a number of important ways. An affidavit is a sworn statement that is documented in writing. Affidavits are usually utilized in court proceedings or in negotiations. The glossary contains definitions of terms most frequently encountered in the collection and reporting of Summary Reporting System data. An affidavit is the written equivalent of verballygiven court testimony. Noun written declaration made under oath; a written statement sworn to be true before someone legally authorized to administer an oath. An affidavit is the written equivalent of verballygiven court testimony. These legal documents are used in conjunction with witness statements or related evidence in a dispute.