Compost is the product resulting from the controlled biological decomposition of organic material.

More specifically, compost is the stable, humus-like product resulting from the biological decomposition of organic matter under controlled conditions. A wide range of materials may be composted, but they must consist of principally organic components (i.e. carbon-containing remnants or residues of life processes). Compost is a valuable soil amendment because it: can improve soil structure, aids in necessary microbial activity in the soil, attracts beneficial insects such as earthworms, can suppress several soil borne diseases and holds its nutrients in organic or slow release form, allowing for their availability throughout the growing season.