A droplet is a tiny, individual drop of liquid, small enough that you can see its round shape. When you sneeze or cough, hundreds of tiny droplets of moisture spray out into the air. When morning dew forms on grass, each blade might hold dozens of perfect little droplets that catch the sunlight like miniature glass beads.

Droplets form because of something called surface tension: the molecules in a liquid naturally pull together into the smallest, most compact shape they can make, which happens to be a sphere. That's why water droplets on a freshly waxed car look like perfect little domes, and why droplets floating in space form perfect spheres.

The word droplet emphasizes smallness. You wouldn't call the water coming out of a faucet a droplet, you'd call it a stream. But the mist from a spray bottle? Those are droplets. Scientists study how droplets behave because understanding them helps explain everything from how clouds form to how diseases spread through the air. Next time it rains, watch how droplets bead up on a leaf or spider web: each one is a miniature world of physics in action.