USCIS.gov now has an online dictionary (glossary). You can use this dictionary to quickly look up a definition or explanation for a topic.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. An affidavit is a written statement. A person, known as the affiant, swears under oath to the statement's truthfulness. Affidavits are normally used in court proceedings or government agencies. An affidavit is a document in which a person gives facts, and swears that the facts are true and accurate. The FindLaw Legal Dictionary -- free access to over 8260 definitions of legal terms. Search for a definition or browse our legal glossaries.