>>53110072>GroundIn Pokemon, Ground can be creatures that burrow (Diglett), have earth powers/control (Ursaluna, Groudon) or things relating to sand (Sandile, Hippowdon) or clay (Runerigus, though I'm with the majority who think it should've been Ghost/Rock).
>RockRock are creatures composed of rock (Nacli), Roggenrola, have rock/mineral adornments (H Growlithe, Rockruff), fossils, crystals (Diancie).
All in all a relatively arbitrary distinction that admittedly can cross lines sometimes, with shit like Runerigus, Sandstorm, etc.