Definition of ground zeros:
(n) :
(by extension) The location of any disaster or violent assault.
(n) :
Originally, the point on the land or water surface below which a nuclear bomb detonates in the air; now also the point on such a surface at or above the detonation.
(n) :
(figuratively) The point at which something begins.
(n) :
The site of the former World Trade Center towers in New York City destroyed on 11 September 2001.