A cage made of plastic, silicone, metal, or another material that fully encompasses a penis. The cage is then locked so it can't be taken off without the key. It's designed to prevent erections & masturbation and is often used in bdsm relationships where the key is given to someone's significant other, called a keyholder. It is still possible to masturbate in them however, either by using a vibrator on the cage or using a dildo in the ass.
Shoddily welded cages of sheet metal used by the Armed Forces of the Russian Federation during their illegal invasion of Ukraine to protect their modern multi-million dollar armored vehicles against $200K Javelin missiles, despite the obvious fact that they'd be as effective as a wet tissue against a sharpened pencil.
"Hey Ivan, I sure hope these Cope Cages will protect us as we invade this innocent country."
"I don't see why not Vlad, it is not like we used anything but the lowest grade steel and spot welded them together!"