Non est factum

The literal meaning of this phrase means it is not my deed is a defence invoked in contract law to escape an effect to a signed document.
In the instance of an agreement involving two or more parties, a party can invoke the non est factum as a defense against the consequences of document signed by virtue of fraud or misrepresentation. In addition, although the party admits to signing the document he can plead non est factum on the grounds that he was defrauded by the other contracting party and not ought to bear the effects of the signed document.