Mineral horizon below an O, A, or E horizon. The B horizon show evidences of soil forming processes which distinguish it from the parent material of soil (underlying C horizon). The distinctive characteristics can be: (1) accumulation (iluviation) of clay, sesquioxides, humus, or a combination of these; (2) granular, prismatic, or blocky structure; (3) redder or browner colours than those in the A horizon; (4) evidences of accumulation of secondary gypsum or carbonates; or (5) a combination of these.

Microscopic, single-celled organisms. They include the photosynthetic cyanobacteria (formerly called blue-green algae), and actinomycetes (filamentous bacteria that give healthy soil its characteristic smell).

A soil food web in which the ratio of fungal biomass to bacterial biomass is less than one.

The degree to which a soil having cation-exchange properties is saturated with exchangeable bases (sum of Ca, Mg, Na, K), expressed as a percentage of the total cation-exchange capacity.

The initial soil condition before monitoring soil quality over time. Subsequent measurements on the same soil are compared to the baseline measurement.

The weight a soil can withstand before severe damage occurs to the structure of the soil. Bearing capacity varies throughout the year, based upon the moisture content of the soil. For instance a very heavy tractor that causes no damage on dry soils may cause a lot of damage to the soil structure of wetted soils.

The solid rock that underlies the soil and other unconsolidated material or that is exposed at the surface.

A benchmark soil is one of large extent, holds a key position in the soil classification system, or is of special significance to farming, engineering, forestry, livestock production, or other uses. The purpose of benchmark soils is to focus data collection and research efforts on soils that have the greatest potential for expansion of data and interpretations.

The diversity of living organisms in any one place.

The multitude of soil organisms and processes, interacting in an ecosystem, making up a significant part of the soil's natural capital, providing society with a wide range of cultural services and unknown services.