1. The calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological. (JP 1-02 and JP 3-07.2).

2. Premeditated, politically motivated violence perpetrated against noncombatant targets by sub-national groups or clandestine agents (22 USC §2656f(d) and the National Strategy for Combating Terrorism, Feb 2003) [Definition used by Department of State, NCTC and CIA].

3. The unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives. (28 CFR §0.85) [Definition used by FBI, which reflects its mission, identifying a terrorist incident as a violation of the criminal laws of the United States and a suspected terrorist would, therefore, be subject to arrest and prosecution.] [The federal crime]: An offense that is calculated to influence or affect the conduct of government by intimidation or coercion, or to retaliate against government conduct. This includes terrorist acts committed within and outside U.S. national boundaries. See 18 USC 2332b(g)(5)(A).

Source: Terms & Definitions of Interest for DoD Counterintelligence Professionals, Office of the National Counterintelligence, https://www.dni.gov/files/NCSC/documents/ci/CI_Glossary.pdf