Clay is a type of Terrian that is brown in color and spawns in a variety of biomes.
Should the player wish to fix or repair any clay terrain, this can be done with 30x Lump of Clay for each block of Clay they wish to repair.
Clay can be found by opening the map (default key 'm') and looking for brown matches of earth.
Clay is also often accompanied by different plants growing nearby. This is most often seen in the Forest Biome.