The trachea is the tube that carries air from your throat down towards your lungs. In everyday English almost nobody says 'trachea' — they say 'windpipe'. 'Trachea' is the doctor's word: you meet it in a hospital, in a biology class, in a textbook. Both words point at the same tube, so if you know 'windpipe' you already know what a trachea is; you are just learning the formal name for it. Two things worth knowing about the word itself. First, the plural is usually 'tracheae', though 'tracheas' is also written and doctors say both. Second, it is one of those words people stress differently — in British English usually truh-KEE-uh, in American English often TRAY-kee-uh — so do not be confused when you hear it two ways. Biology uses the word beyond humans too: insects breathe through a network of tiny tubes, and each of those is called a trachea as well.