The term ground zero (sometimes also known as surface zero as distinguished from zero point) describes the point on the Earth's surface closest to a detonation. In the case of an explosion above the ground, ground zero refers to the point on the ground directly below the detonation (see hypocenter).
The term has often been associated with nuclear explosions and other large bombs, but is also used in relation to earthquakes, epidemics and other disasters to mark the point of the most severe damage or destruction. The term is often re-used for disasters that have a geographic or conceptual epicenter.
Trinity, Hiroshima, and Nagasaki 
The origins of the term ground zero began with the Manhattan Project and the bombing of Japan. The Strategic Bombing Survey of the atomic attacks, released in June 1946, used the term liberally, defining it as: "For convenience, the term 'ground zero' will be used to designate the point on the ground directly beneath the point of detonation, or 'air zero.'" William Laurence, an embedded reporter with the Manhattan Project, reported that "Zero" was "the code name given to the spot chosen for the atomic bomb test" in 1945.
The Oxford English Dictionary, citing the use of the term in a 1946 New York Times report on the destroyed city of Hiroshima, defines ground zero as "that part of the ground situated immediately under an exploding bomb, especially an atomic one."
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. At Hiroshima, the hypocenter of the attack was Shima Hospital.
The Pentagon 
The Pentagon, the headquarters of the U.S. Department of Defense in Arlington, Virginia, was thought of as the most likely target of a nuclear missile strike during the Cold War. The open space in the center is informally known as ground zero, and a snack bar located at the center of this plaza was nicknamed "Cafe Ground Zero".
World Trade Center 
Since 2001 in the United States, especially in the media, "Ground Zero" is generally understood to mean the site of the World Trade Center, which was destroyed in the September 11 attacks. The phrase was being applied to the World Trade Center site within hours after the towers collapsed. It appears that the first use of the term on a mainstream North American media outlet in reference to the September 11 attacks was at approximately 11:55 am when an eye witness who claimed to be a Fox News freelancer referred twice to ground zero. He may also have been the first person to suggest the cause of the collapse of the towers was due to "structural failure due to fires". At 4:41 p.m., in an interview with Peter Jennings on ABC News, attorney and survivor of the attacks Tom Humphreys (spelled "Humphries" on air) said, in reference to the collapse of the South Tower, that
|“||The tragedy is that the police and fire personnel that tried to help people out of that building were right at Ground Zero when that happened...||”|
|“||Less than four miles behind me is where the Twin Towers stood this morning. But not tonight. Ground Zero, as it's being described, in today's terrorist attacks that have sent aftershocks rippling across the country.||”|
|“||We're now just a block away from the World Trade Center and the closer we get to "ground zero" the harder it is to breathe and to see.||”|
Rescue workers also used the phrase "The Pile", referring to the pile of rubble that was left after the buildings collapsed. Even years later, the term "Ground zero" has become a shorthand for the site, even after construction on the new One World Trade Center and the National September 11 Memorial & Museum were well underway. In advance of the 10th anniversary of the attacks, New York City mayor Michael Bloomberg urged that the "Ground zero" moniker be retired, saying, "... the time has come to call those 16 acres what they are: The World Trade Center and the National September 11th Memorial and Museum."
- Military Dictionary - Terms Defined "Surface Zero"
- Military Dictionary - Terms Defined "Zero Point" Note: The zero point may be in the air, or on or beneath the surface of land or water, depending upon the type of burst, and it is thus to be distinguished from ground zero.
- Nuclear Matters: A Practical Guide, Appendix B
- U. S. Strategic Bombing Survey: The Effects of the Atomic Bombings of Hiroshima and Nagasaki. June 19, 1946. President's Secretary's File, Truman Papers. Page 5.
- William L. Laurence, Dawn over Zero (London: Museum Press, 1947), 4.
- "Pentagon Hot Dog Stand, Cold War Legend, to be Torn Down". United States Department of Defense. September 20, 2006. Retrieved 2010-05-06. "'It's rumored that a portion of their (Soviet) nuclear arsenal was directed at that building, the Pentagon hot dog stand,' tour guides tell visitors as they pass the stand. 'This is where the building earned the nickname Cafe Ground Zero, the deadliest hot dog stand in the world.'"
- FOX News - Rick Leventhal interviews 9/11 WTC witness, Mark "Harley Guy" Walsh (uploaded to YouTube by YouTube user Gideon52480 on November 23, 2010). Fox news. 11 September 2001. Retrieved 11 September 2011. "(1:31-1:38)...then I witnessed both towers collapse, first one then the second, mostly due to structural failure because the fire was just too intense... (1:45-1:50)...those guys were all right there at ground zero when those things went down..."
- September 11 Television Archive
- CBS 9, Washington, D.C., at Internet Archive's September 11 Television Archive. Kathleen Matthews, of WJLA, Washington, D.C. said at 7:02 p.m. EDT, "Ground Zero for the terrorist attack here in the Washington area is of course The Pentagon." September 11 Television Archive.
- Rehema Ellis's report on NBC using the term "Ground Zero" at the Internet Archive
- Hamill, Denis (16 September 2001). "Rescue Workers Keep Up Quest for Signs of Life Ruin All Over, But Not One Unkind Word". Daily News (New York).
- Geoghegan, Tom (2011-07-Sep). "Is it time to retire 'Ground zero'?". BBC. Text "2011-10-Sep" ignored (help)