backplate

Short definition from Wiktionary

Noun

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