A corpuscle is a tiny cell or particle in your body, especially one of the blood cells that flow through your veins and arteries. The two main types are red corpuscles (which carry oxygen from your lungs to every part of your body) and white corpuscles (which help fight off germs and infections).

These cells are so small you need a microscope to see them. A single drop of blood contains millions of red corpuscles, all working together to keep you alive and healthy. When a doctor orders a blood count, they're measuring how many corpuscles you have, since having too many or too few can signal health problems.

While “corpuscle” sounds old-fashioned (doctors today usually just say “blood cell”), you'll still encounter it in science books and historical medical writing. Scientists also use the term for other tiny structures in the body, like tactile corpuscles, which are microscopic structures in your skin that help you feel touch and pressure.