Mucus is a thick, slippery liquid that the body makes to keep wet places wet and to catch dirt and germs. You know it best from your nose — that sticky stuff when you have a cold — but the same kind of liquid is made in the mouth, the throat, the lungs, and the gut. Doctors and medicine labels say mucus in a calm, medical way. Everyday English is ruder about the nose: people say snot, which sounds childish or a bit gross. Mucus itself is not a rude word. The body is supposed to make it; we only complain when there is too much, as with a cold or allergies. Though actually, the mucus in your nose and the thicker stuff you cough up from the chest are not talked about the same way — the chest stuff is often called phlegm.