The National Counterterrorism Center (NCTC) is a U.S government agency responsible for national and international counterterrorism efforts.

The FBI National Crime Information Center (NCIC) 2000 is a nationwide information system dedicated to serving and supporting criminal justice agencies -- local, state, and federal -- in their mission to uphold the law and protect the public. (Source: FBI)

October has been designated as National Cyber Security Awareness Month by the U.S. Department of Homeland Security.

The National Infrastructure Advisory Council provides the President, through the Secretary of Homeland Security, with advice on the security of critical infrastructures, both physical and cyber, supporting sectors of the economy. (Source: DHS)

See: National Security Act of 1947.

The National Security Act of 1947, signed by President Harry S. Truman, mandated a reorganization of U.S. foreign policy and military establishments, and created the National Security Council (NSC), Central Intelligence Agency (CIA) and the Office of the Director of Central Intelligence (DCI).

The National Security Agency/Central Security Service is America’s cryptologic organization. It coordinates, directs, and performs highly specialized activities to protect U.S. government information systems and produce foreign signals intelligence information. (Source: NSA)

The National Security Council is the President's principal forum for considering national security and foreign policy matters with his senior national security advisors and cabinet officials. Since its inception under President Truman, the function of the Council has been to advise and assist the President on national security and foreign policies. The Council also serves as the President's principal arm for coordinating these policies among various government agencies. (Source: Whitehouse.gov)

The U.S. Department of Homeland Security designates certain events, such as presidential inaugurations and conventions as National Special Security Events.

North Atlantic Treaty Organization.

Refers to the long-term host of the pathogen of an infectious disease. It is often the case that hosts do not get severely ill. (Source: DHS)

See: National Crime Information Center (NCIC).

National Counterterrorism Center.

See: National Counterterrorism Center (NCTC).

Northeast Air Defense Sector.

Non-Governmental Organization.

See: National Infrastructure Advisory Council (NIAC).

North American Aerospace Defense Command.

See: National Security Agency (NSA).

National Transportation Safety Board.

The energy released in the detonation of a nuclear weapon, measured in terms of the kilotons or megatons of trinitrotoluene required to produce the same energy release. Yields are categorized as follows: very low--less than 1 kiloton; low--1 kiloton to 10 kilotons; medium--over 10 kilotons to 50 kilotons; high--over 50 kilotons to 500 kilotons; very high--over 500 kilotons. See also nominal weapon; subkiloton weapon. (Source: DOD)

New York Police Department.