An affidavit is a statement sworn before a Notary Public or Attorney, which is verified by the Notary individual to attest that the person swearing to the statement is the person whose signature appears at the notarization section, and mentioned in the letter itself. It is confirmation that the person drafting the statement is real, and verifies through proper identification that they are the person mentioned in the Affidavit.
An Affidavit can be short, or lengthy, depending on what is contained in the statement. The most important part of the Affidavit is that the person relying on the statements made knows that it has been verified, and properly notarized by the person or individual signing it.