induration. 1. the process of hardening or being hardened.
1 They're weak against the Ice and Water types in reference of erosion, which cause this elements to the ground. 2  They're immune against the Electric type because in real life, the ground is a natural sink of electrons.  The Bug type resists them because many bugs like worms live inside the ground and many of them eat it.
Earth Fault Protection, also known as Protective Earth Ground, also known as the Grounding Conductor, or more simply, just Ground, is a connection ultimately to a system of grounding rods that are driven into the earth.