Which of the following best describes an affidavit?

An affidavit is best described as a written statement made under oath. This legal document is typically used to present evidence in court and is sworn to be true by the individual making the statement, who is known as the affiant. The formal, sworn nature of an affidavit carries significant weight in legal proceedings, as it serves to provide factual information or testimony that can be relied upon by the court.

The other options do not accurately capture the essence of an affidavit. A verbal statement given in court refers to oral testimony, which is distinct from the written format of an affidavit. A letter outlining legal arguments does not involve an oath and is typically less formal than an affidavit. Lastly, a casual agreement between parties lacks the solemnity and formal structure required of legal affidavits, which must meet specific procedural requirements to be valid in legal contexts.