A droplet is a very small drop of liquid — smaller than the drops you watch on a window in the rain. People use it for a little drop of water, oil, blood, or medicine. Scientists talk about droplets in clouds, and doctors talk about the tiny droplets that fly out when someone coughs or sneezes (that is “droplet spread”). It sounds a little more careful than “tiny drop,” and it is at home in science class, but it is not a hard word. It is a count noun: one droplet, two droplets.