a group of soils in the broadest category, differentiated by the presence or absence of diagnostic horizons; in the current US system of soil taxonomy there are 11 soil orders: Alfisol, Andisol, Aridisol, Entisol, Histosol, Enceptisol, Mollisol, Oxisol, Spodosol, Ultisol, and Vertisol —see alluvial soil, intrazonal soil, pedalfer, pedocal, zonal soilThis definition last updated 10/07/2008