What does the term "non est factum" mean in contract law?

The term "non est factum" translates from Latin to "that is not my deed" and is a principle in contract law. It refers to a defense that a party can use to argue that they should not be bound by the terms of a contract because they did not understand the nature or consequences of the document they signed, often due to factors such as mental incapacity, fraud, or misrepresentation. This principle is significant in situations where a party claims that the document does not reflect their true intention or understanding.

By asserting "non est factum," individuals aim to demonstrate that they lack the necessary understanding to be held accountable for a contract that may have significant legal implications. This defense is particularly relevant in cases where the signatory might have been misled or unable to comprehend what they were signing.

The other options address different concepts in contract law, such as unfair contracts, legally binding agreements, and contracts made under duress, but none capture the specific essence and application of "non est factum" as accurately as the identification of it as a claim of misunderstanding or unawareness regarding the nature of the deed itself.