Soil is a complex mixture of minerals, water, air, organic matter, and countless organisms that together support the life of plants and soil organisms. It forms at the surface of land and is often referred to as the "skin of the earth". Soil is capable of supporting plant life and is vital to life on earth. It provides the structural support to plants used in agriculture and is a product of several factors, including climate, relief, organisms, and the soils parent materials interacting over time.

Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution) . Accordingly, soil is a three-state system of solids, liquids, and gases. The solid part of the soil is made up of particles such as organic matter, silt, sand, and clay which form aggregates. Aggregates are held together by clay particles and organic matter. Organic matter is one of the major cementing agents for soil aggregates. The size and shape of aggregates give soil a characteristic called soil structure. Soil structure influences plant growth by affecting the movement of water, air, and nutrients to plants.

Soil performs many critical functions in almost any ecosystem, including sustaining plant and animal life, regulating water flow, filtering and buffering pollutants, cycling nutrients, and providing physical stability and support. There are seven general roles that soils play, including serving as media for growth of all kinds of plants, modifying the atmosphere by emitting and absorbing gases, providing habitat for animals that live in the soil, and absorbing, holding, releasing, altering, and purifying most of the water in terrestrial systems.

In summary, soil is a complex mixture of minerals, water, air, organic matter, and countless organisms that together support the life of plants and soil organisms. It provides the structural support to plants used in agriculture and performs many critical functions in almost any ecosystem.