In the terminology of the United States Environmental Protection Agency (EPA), a Concentrated Animal Feeding Operation (CAFO) is an animal feeding operation (AFO) that (a) confines animals for more than 45 days during a growing season, (b) in an area that does not produce vegetation, and (c) meets certain size thresholds. The EPA's definition of the term "captures key elements of the transformations" observed in the animal agriculture sector over the course of the 20th century: "a production process that concentrates large numbers of animals in relatively small and confined places, and that substitutes structures and equipment (for feeding, temperature controls, and manure management) for land and labor."