Microscopic means so small that you need a microscope to see it clearly. A grain of salt looks tiny to your naked eye, but microscopic things are thousands or even millions of times smaller than that. Bacteria, individual cells in your body, and the tiny organisms living in a drop of pond water are all microscopic.

Scientists use powerful microscopes to study this hidden world. When they examine a sample of your blood under a microscope, they can see individual red blood cells floating past, even though millions of them fit in a single drop. The invention of the microscope in the 1600s revolutionized science by revealing that entire universes of life existed at scales humans had never imagined.

People also use microscopic informally to mean extremely small, even if they don't literally need a microscope. If you tear your paper and make a microscopic rip, you mean it's barely visible. If someone gives you a microscopic piece of cake, they gave you a disappointingly tiny slice.