The area surrounding the World Trade Center became the site of the greatest number of casualties and missing, and physical destruction. This region became known in the ensuing days as "ground zero".Ground zero is the exact location on the ground where any explosion occurs. The term has often been associated with nuclear explosions, but is also used in relation to earthquakes, epidemics and other disasters to mark the point of the most severe damage or destruction. Damage gradually decreases with distance from this point.The term may also be used to describe the impact point of any exploding bomb. In the case of a bomb which explodes above ground, the term refers to the point on the ground directly below the bomb at the moment of detonation (see hypocenter).The term was military slang—used at the Trinity site where the weapon tower for the first nuclear weapon was at point 'zero'—and moved into general use very shortly after the end of World War II.