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.
Fighting Type Good against: Normal, Ice, Rock, Dark, Steel Bad against: Poison, Flying, Bug, Ghost , Psychic. Fire Type Good against: Grass, Ice, Bug, Steel Bad against: Water, Fire, Dragon, Rock. Flying Type Good against: Grass, Fighting, Bug Bad against: Electric, Rock, Steel. Ghost Type Good against: Ghost, Psychic Bad against: Dark, Steel. Grass Type Good against: Water, Ground, Rock Bad against: Fire, Grass, Poison, Flying, Bug, Dragon, Steel