That means that they eat dead things. Because of their dietary habits, fungi are very important to our ecosystem. If it weren't for them, we'd be up to our necks in litter and garbage. Fungi come in many shapes and sizes, from the very large to the microscopic. But what is most important to me is that you can eat them.
Commercial mushroom growing is big business in the United States.
Commercial growers produce mushrooms in large trays filled with horse manure or a synthetic compost. After a suitable time period, the fungus will produce a mushroom which will appear above the surface and can be harvested. While there are a few species of easily identifiable edible mushrooms, the largest percentage of wild mushrooms are dangerous to eat. Eating them can cause you to get very sick, hallucinate, or in some cases die. An experienced mushroom hunter can point out species like morels, inky caps, or oyster mushrooms, but it's best not to risk it if you don't know what you're doing.