The FindLaw Legal Dictionary -- free access to over 8260 definitions of legal terms. Search for a definition or browse our legal glossaries.They have a terrible title, and they are full of legalese. Complete both pages of the Affidavit of Financial Support form and provide documentation as required. Rule 101 Scope; Definitions. 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. It must be signed or acknowledged in front of a notary. This sworn legal document serves as evidence in both civil and criminal cases and is used to support or challenge a claim. For complete results, pick the county where your case is (or will be) filed.