Fungi are heterotrophic eukaryotes with cell walls that contain chitin, a compound also found in the shells of several members of the animal kingdom, including crabs, insects, and shrimp. Although fungi are multicellular and have some cellular differentiation, the degree of cellular specialization is not great. Many fungi obtain their food from dead organic matter such as plants or animals. Such fungi are saprophytic. Other fungi may absorb the complex molecules they need from living organisms. If such fungi harm the living organism from which they obtain their nutrients, the fungi are considered to be parasites. Common examples of fungi include mushrooms (both edible and poisonous), athlete's foot, mold on moldy bread, blue veins in blue cheese, Bakers' Yeast, jock itch, and yeast infection.
In older classification systems, fungi were defined as "plants without chlorophyll." That is not a valid definition for fungi in today's five-kingdom system.