Which document is defined as a written statement made under oath?

An affidavit is a written statement made under oath, which means that the person making the statement has sworn to its truthfulness before an authorized person, such as a notary public or a court. This document serves as a way to present factual information in a legal context, often used in court proceedings or to support various legal matters. The key aspect of an affidavit is the under-oath requirement; it attaches a level of seriousness and legality to the claims made within the statement.

In contrast, a will is a legal document that outlines how a person's assets will be distributed after their death, without the requirement of being made under oath. Deed essentials refer to the necessary components that must be present for a deed to be valid, which typically does not include an affidavit format. A title is a legal right of ownership over property, but again, it is not a written statement made under oath.

Thus, the definition of an affidavit distinctly matches the characteristics described in the question, confirming it as the correct answer.