What is the electrical terminology meaning of earth?

Answer 1

In electrical terminology the earth is a wire that connects the outer metal cases of all items electrical equipment together so that a user will not receive a shock from them. The earth wire is also connected to water pipes and gas pipes at each property, and to an earth rod in the ground to allow any static charge from the atmosphere to go to ground.

In certain fault conditions an internal live wire might come into contact with the case of a piece of equpiment, and in that case the earth wire provides a path for the fault current to flow and cause the fuse or circuit-breaker to operate, restoring a safe condition.

The earth wire is a third wire separate from the two current-carrying wires, the live and neutral.