The windpipe is the tube that carries air from your throat down into your lungs. Put your fingers on the front of your neck and press gently — that firm ridged tube is it. Doctors call it the trachea; everyone else says windpipe. That is the useful thing about this word: it is the plain, everyday name for a body part that also has a hard Latin name, so you can use it with anybody and be understood. It turns up most often when something goes wrong — food going down the wrong way, a blow to the throat, choking: 'the food went into his windpipe', 'she grabbed him by the windpipe'. Because the throat carries two tubes side by side (one for air, one for food), the word is often used to explain that pair. In older or rougher speech people say things like 'I'll rip your windpipe out', which tells you it also carries a slightly violent, physical flavour in fiction. Note that it is a body word, not a machine word — a pipe carrying wind in a building is a duct or a vent, never a windpipe.