A germ is a tiny living thing, so small you can't see it without a microscope, that can sometimes make you sick. Germs include bacteria and other microscopic organisms that spread from person to person or from surfaces to your hands. When someone sneezes without covering their mouth, they spray germs into the air. When you touch a doorknob that a sick person just touched, germs can transfer to your fingers.

Not all germs are harmful. Your body contains trillions of helpful bacteria that aid digestion and keep you healthy. But the germs people usually worry about are the ones that cause colds, flu, strep throat, and stomach bugs. That's why washing your hands with soap matters: soap helps water rinse germs away before they can enter your body through your mouth, nose, or eyes.

The word germ can also mean the beginning or origin of something, like when a germ of an idea starts forming in your mind. This meaning connects to how germs grow and multiply: a single germ can rapidly reproduce into millions, just as one small idea can develop into something much bigger.