Protective metal plate for armor.
Also known as a trauma plate, these plates are used to absorb the kinetic energy of whatever might be coming at it, such as a bullet or a club. Most trauma plates are made with a variety of materials, but metal is a common material used. There are rumors of bullets deflecting off the metal plate and injuring the wearer, usually by hitting them in the head. While these claims are unverified, most plates are encased in materials designed to trap bullets to address this fear.
Can be found in ballistic vests.