backplate

noun6

1. •
   A plate harnessed to a diver's back, to which the gas cylinders are attached.
2. •
   The metal plate on the rear of a computer's casing, where the ports are found.
3. •
   A wood or metal (or glass, etc) plate that serves as a backing for an object.
4. •
   (UK) A rigid metal plate inside the brake drum, which supports the wheel cylinder, brake shoes, and other parts of a drum brake.
5. •
   Part of a condenser microphone that sits behind the diaphragm and which acts, in conjunction with the diaphragm, as a sort of variable capacitor.
6. •
   A plate protecting a fighting person's back.

   • The cuirass of Roman muscled type is composed of an anatomically modeled breastplate and backplate, each made in one with a gorget […] — 1998