Agaricus bisporus
The term refers to the stereotypical view of mushroom cultivation, where mushrooms are "kept in the dark and periodically given a load of manure". In fact, the most commonly cultivated mushroom, "Agaricus bisporus", is grown on a pasteurized compost substrate, not raw manure (common raw ingredients in mushroom compost are horse manure and straw). The chemical and microbiological nature of finished compost is, however, quite different from raw manure.