What is the legal term for a voluntary written statement made under oath?

The legal term for a voluntary written statement made under oath is an "affidavit." An affidavit is used as a means of presenting evidence in court or legal proceedings, and it must be signed by the affiant (the person making the statement) in the presence of a notary public or another authorized official. This document attests to the truth of the statements made within it, making it a crucial element in various legal contexts.