The term microbial refers to anything related to or involving microorganisms, which are tiny organisms that can only be seen with a microscope. These include bacteria, fungi, viruses and some protozoa. Microbes play an important role in many natural processes such as decomposition of dead plants and animals, nitrogen fixation, and the production of certain foods like yogurt or cheese through fermentation. The term microbial can also be used to describe a substance that is produced by or contains microorganisms, for example "microbial growth" refers to the growth of microbes in a particular environment.