"Nulidade da patente" is the term used by the Brazilian Intellectual Property Act (Law No. 9,279 of 1996) to describe the situations in which a patent can be considered invalid (sec. 46 - 57, of the law).
a defence against a patent infringement claim where the defendant claims that the product or process is a prior art (=generally known at the time that the patent was granted) and that the patent is therefore invalid on the grounds of novelty. The defence is named after the case of Gillette Safety Razor V Anglo Trading Case (1913).
The defendant used the 'Gillette defence' as a defence strategy to safeguard its interest in a patent infringement suit.