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. Section 2003 - Affidavit.An affidavit is a written declaration under oath, made without notice to the adverse party. An affidavit is a written statement in which the signer or "affiant" verifies that the document is true. An affidavit is a written statement made under oath or affirmation. It's used as evidence in legal proceedings. In a nutshell, an affidavit is a sworn statement that is documented in writing. It is a legal document detailing knowledge the person has or facts as they know them to be. Signing an affidavit means you create a legally-binding written statement. That gives a document legal power and is important in a wide range of areas.