noun

1. A plate protecting a fighting person's back.

2. (underwater diving) A plate harnessed to a diver's back, to which the gas cylinders are attached.

3. A metal plate on the rear of a computer's casing, used to cover a port or slot.

4. A wood or metal plate that serves as a backing for an object.

5. A rigid metal plate inside the brake drum, which supports the wheel cylinder, brake shoes, and other parts of a drum brake.

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.