It comes from a past tense form of the Latin verb affidare, meaning "to pledge"; in Latin, affidavit translates to "he or she has made a pledge. A written statement that someone makes after promising officially to tell the truth.An affidavit can be used as proof in a law court. I, the undersigned, declare that the information I have provided on this form is true and accurate. An affidavit is a written statement made under oath or affirmation.