A dum-dum is a kind of bullet made so that it does not stay neat when it hits a body. The front is soft, or it is built to open, so the metal spreads or breaks into pieces. That makes a much bigger, messier wound than a smooth, hard bullet that goes in small and may even pass through. People also call this an expanding bullet or a hollow-point; dum-dum is the older, slightly newspaper-ish name. Though actually, soldiers and lawyers are picky here: in international war, this kind of bullet has been banned for a long time, because it is meant to wreck flesh, not just stop a person. Police in some countries still use expanding bullets on the street, with a different argument — they want the bullet to stay in the body so it does not fly on and hit someone else. The name is not from the English word dumb. It comes from Dum Dum, a place near Kolkata in India, where a British arsenal made this type of bullet. You will meet it in history, news about weapons, and crime stories. It is not everyday talk.