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.
In Naruto each base-element is stronger and weaker than one element:-. 1  Fire: strong against Wind, weak against Water. 2  Wind: strong against Lightning, weak against Fire. 3  Lightning: strong against Earth, weak against Wind.  Earth: strong against Water, weak against 1  Lightning. Water: strong against Fire, weak against Earth.