To cough means to force air suddenly and noisily out of your lungs through your throat and mouth. Your body does this automatically when something irritates your airways: dust, smoke, or mucus from a cold. Coughing is your body's way of clearing your breathing passages, like a built-in cleaning system.

When you have a cold or the flu, you might develop a persistent cough that lasts for days. Sometimes a cough is dry and harsh, sometimes it's wet and produces mucus (which people call phlegm). Doctors pay attention to what kind of cough you have because it helps them figure out what's wrong.

The word also describes the sound itself: you might hear someone cough in a quiet library. People sometimes cough deliberately to get attention or signal something, like when a teacher gives a pointed cough to quiet down a noisy classroom. This kind of cough is called a polite cough or discreet cough.

The phrase cough up has an informal meaning too: to give something reluctantly, usually money. If your friend owes you five dollars, you might say, “Come on, cough it up!”