Compost

Decaying plant material which is added to earth to improve its quality. - A mixture for fertilizing land; esp., a composition of various substances thoroughly mingled and decomposed, as in a compost heap. - Composting is the transformation of organic material (plant matter) through decomposition into a soil-like material called compost. Invertebrates (insects and earthworms), and micro-organisms (bacteria and fungi) help in transforming the material into compost. Composting is a natural form of recycling, which continually occurs in nature.

(Source: http://www.oldgrowth.org/compost/ )