A microbe, or “microscopic organism,” is a living thing that is too small to be seen with the naked eye. We need to use a microscope to see them.
The term is very general. It is used to describe many different types of life forms, with dramatically different sizes and characteristics:
The human body is home to microbes from all of these categories. Microscopic plants are also considered microbes, though they don’t generally live on or in the human body.