Compost is the aerobically decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture as a soil amendment, and commercially by the landscaping and container nursery industries. It is also used for erosion control, land / stream reclamation, wetland construction, and as landfill cover. Compost is also used as a seed starting medium generally mixed with a small portion of sand for improved drainage.

Given enough time, all biodegradable material will compost. However, not all compost feedstocks are appropriate for backyard composting. Most backyard systems will not reach high enough temperatures to kill pathogens or deter vermin, so pet droppings, non-vegetarian animal manure, meat scraps, and dairy products are best left to operators of high-rate, thermophylic composting systems.

Compost is a versatile, easy-to-use product. When manufactured to meet United States Environmental Protection Agency Class A standards, compost is safe to use around children and pets and can be applied to crops at any point in the production cycle. Homemade compost can also be applied without restriction, provided only plant materials (residential yard waste, vegetable scraps, etc.) have been incorporated as feedstocks and no lingering chemicals have been used to grow the plants.