What is Informatus Non Sum?

Legal Definition
Pleading, practice. I am not informed; a formal answer made in court, or put upon record by an attorney when he has nothing to say in defence of his client. Styles Reg. 372.
-- Bouviers Law Dictionary
Legal Definition
In practice. I am not informed. A formal answer made by the defendant's attorney in court to the effect that he has not been advised of any defense to be made to the action. Thereupon judgment by default passes.
-- Black's Law Dictionary
Legal Definition
I am not informed, a judgment resembling a default, entered by the defendant, usually by agreement. See 3 Bl. Comm. 397.
-- Ballentine's Law Dictionary