The meaning of earthing

It is a fundamental fact that electricity ALWAYS flows to the point of lowest potential. The task is to ensure that electricity, including faults, lightning and electronic noise, and flows to this point with maximum safety to people, while maintaining the reliability of equipment. Therefore we must ensure the safe, controlled flow of electricity with minimum voltage drop to earth in all cases.

The different between earth and ground 

  Ground:

The NEC, National Electrical Code defines a ground as: A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.

Earth:

The conductive mass of the earth, whose electric potential at any point is conventionally taken as equal to zero. (In some countries the term "ground" is used instead of "earth.")