Soil is a natural body that consists of layers (soil horizons), composed primarily of minerals, which differ from their parent materials in their texture, structure, consistency, color, chemical, biological and other physical characteristics. The end result, soil, is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), temperature, and time. In engineering, soil is referred to as regolith, or loose rock material. Strictly speaking, soil is the depth of regolith that influences and has been influenced by plant roots and may range in depth from centimeters to many meters.

Soil is composed of particles of broken rock (materials) that have been altered by chemical and mechanical processes that include weathering, erosion and precipitation. Soil is altered from its parent material by the interactions between the lithosphere, hydrosphere, atmosphere, and biosphere. It is a mixture of mineral and organic materials that are in solid, gaseous and aqueous states. Soil is commonly referred to as earth or dirt; technically, the term dirt should be restricted to displaced soil.