Compost is decomposed organic material, which can be used as a fertilizer and soil amendment.
Composting is done by piling up a collection of organic material (kitchen scraps, garden waste, lawn clippings, manures, etc) and allowing it to rot, typically for a year or more. The composting process can be accelerated by monitoring and managing the feedstock, the size and temperature of the pile, air and water infiltration into the pile, and various other factors.
The raw materials break down into a nutrient rich material via a combination of bacteria, fungi, and other organisms.
Finished compost is useful as a fertilizer, soil amendment, and for erosion control.