Microorganism

They are small living beings with the ability to survive in organic substrates (faeces, dirt, cloudy waters, etc.). They can also infect an animal and, usually, proliferate very quickly. Some of them can cause diseases, these are pathogenic microorganisms.

There are many kinds of microorganisms, including bacteria, viruses, protozoa, fungi, some parasites, etc. They are called microorganisms because they can only be seen using a microscope. They are known, in common language, as microbes/germs.