That means a bomb from a world war (there have been more than one, you see). You know, like the one they just found in London forcing the closure of its City Airport today?
Please note here: It is a bomb from a world war. It is not an American or a British bomb. Nor is it a French or a Soviet bomb. It goes without saying that it certainly could not be a German bomb because it is a bomb from a world war, OK? Why somebody would bury it there like that is hard to say and no one knows who did it, either. So move along, please. Nothing to see here. Weltkriegsbombe, got it?
Bauarbeiter haben im Osten Londons eine Bombe aus dem Zweiten Weltkrieg entdeckt.