Organic matter, also called organic material, consists of organic compounds that have come from the remains and excretions of animals, plants and other organisms. Another definition is biological material that is in the process of decomposing, mainly due to the action of bacteria and fungi. This contrasts with inorganic matter, which is not a product of organisms and their decomposition.
Organic matter is composed around carbon atoms and is biodegradable, whereas inorganic matter centers around other elements and is not biodegradable. Inorganic matter is generally noncombustible and non-volatile. A major exception is fossil fuels, which originated from organic matter but have been heavily transformed over millions of years by tremendous pressure and heat so that their chemical and physical properties differ greatly from those of conventional organic matter. Another exception is lime, or calcium carbonate, which contains calcium, carbon and oxygen.
Organic matter is an important component of soil because it allows the soil to hold water and nutrients essential for plant growth. Humus is the stable form of organic matter for which the decomposition has already been completed and in which there is no longer any major microbial activity.