Definitions for earth plate
An electrode, in the form of a metal plate buried in external soil, used to earth the electrical system of a building
The Standard Electrical Dictionary
A plate buried in the earth to receive the ends of telegraph lines or other circuits to give a ground, q. v. A copper plate is often used. A connection to a water or gas main gives an excellent ground, far better than any plate. When the plate oxidizes it is apt to introduce resistance.