A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. toadstool generally denotes one poisonous to humans.the standard for the name "mushroom" is the cultivated white button mushroom, agaricus bisporus; hence the word "mushroom" is most often applied to those fungi (basidiomycota, agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae, sing. lamella) on the underside of the cap. "mushroom" also describes a variety of other gilled fungi, with or without stems, therefore the term is used to describe the fleshy fruiting bodies of some ascomycota. these gills produce microscopic s...

Source: Wikipedia