A mushroom's the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom"'s the cultivated white button mushroom, Agaricus bisporus, hence the word mushroom's most often applied to those fungi (Basidiomycota, Agaricomycetes) that've a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) on the underside of the cap, just as do store-bought white mushrooms. The word "mushroom" can also be use… (More on Mushrooms)