Microorganism
Microorganism explained in an easy to understand way:

Imagine trying to find your misplaced keys in a cluttered room. Just as you need to sift through and focus on the tiny details among the mess to spot the keys, scientists use microscopes to see microorganisms, like bacteria, amidst the vastness of the unseen world. The connection is that both scenarios require tools and techniques to identify and focus on something small and elusive within a larger, overwhelming context.
Practice Version

Microorganism: A very small organism that can only be seen with a microscope, like bacteria, is a microorganism. A microorganism is a tiny living thing that can be found everywhere, and it includes bacteria, viruses, and fungi.