An agaric (/ /,) is a type of mushroom fungus fruiting body characterized by the presence of a pileus (cap) that is clearly differentiated from the stipe (stalk), with lamellae (gills) on the underside of the pileus. "Agaric" can also refer to a basidiomycete species characterized by an agaric-type fruiting body. Archaically agaric meant 'tree-fungus' (after Latin agaricum); however, that changed with the Linnaean interpretation in 1753 when Linnaeus used the generic name Agaricus for gilled mushrooms.
Most species of agarics are within order Agaricales in the subphylum Agaricomycotina. The exceptions, where agarics have evolved independently, feature largely in the orders Russulales, Boletales, Hymenochaetales and several other groups of the overarching phylum Basidiomycetes. Old systems of classification place all agarics in the Agaricales and some (mostly older) sources use "agarics" as the colloquial collective noun for the Agaricales. Contemporary sources now tend to use the term euagarics to refer to all agaric members of the Agaricales. "Agaric" is also sometimes used as a common name for members of the genus Agaricus, as well as for members of other genera; for example, Amanita muscaria is sometimes called "fly agaric".