A fungus is a type of living organism that survives from drawing nourishment from another living organism, decomposing it at the same time. Mushrooms are a type of fungus typified by a large fruiting body. Mold is a type of fungus characterized by small multi-cellular filaments that thrive where moisture and organic material are plentiful.
Most fungal diseases are found in the tropics, but there are several that are common in northern climates. However, fungal infections in the Western world are rare and, as a result, difficult to diagnose.