The name of a plea by which the defendant says that the deed which he has executed is not his own or binding upon him, because of some circumstance which shows that it was not intended to be his deed, or because it was not binding upon him for some lawful reason; as, when the defendant delivered the deed to a third person as an escrow to be delivered upon a condition, and it has been delivered without the performance of the condition, he may plead non est factum, state the fact, of the conditional delivery, the non-performance of the condition, and add, and so it is not his deed; or if the defendant be a feme covert, she may plead non est factum, that she was a feme covert at the time the deed was made, and so it is not her deed.