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.
Here are a few : Normal is weak against fighting / ghost Fire is weak against water / ground Watâ¦er is weak against grass / electric Grass is weak against flying / fire Flying is weak against electric / ice Ground is weak against grass / water / steel Fighting is weak against psychic / flying Ice is weak against fire Electric is weak against ground ...