Terrorism is difficult to define, even the various law enforcement branches of the U.S. government cannot agree on one single definition. The old adage, "One man's terrorist is another man's freedom fighter" is still very much alive and well today.
Listed below are several definitions of terrorism:
Terrorism is the use or threatened use of force designed to bring about political change.
Brian Jenkins, Senior Advisor to the President (RAND Corp.)
Terrorism constitutes the illegitimate use of force to achieve a political objective when innocent people are targeted.
Walter Laqueur, Professor/Historian/Political Commentator
Terrorism is the premeditated, deliberate, systematic murder, mayhem, and threatening of the innocent to create fear and intimidation in order to gain a political or tactical advantage, usually to influence an audience.
James M. Poland, Author - "Understanding Terrorism"
Terrorism is the unlawful use or threat of violence against persons or property to further political or social objectives. It is usually intended to intimidate or coerce a government, individuals or groups, or to modify their behavior or politics.
Vice-President's Task Force, 1986
Terrorism is the unlawful use of force or 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.
Federal Bureau of Investigation (FBI)
Terrorism is 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.
U.S. Department of Defense (DoD)
Terrorism is all criminal acts directed against a State and intended or calculated to create a state of terror in the minds of particular persons or a group of persons or the general public.
League of Nations, 1937
Terrorism is any act or threat of violence, whatever its motives or purposes, that occurs in the advancement of an individual or collective criminal agenda and seeking to sow panic among people, causing fear by harming them, or placing their lives, liberty or security in danger, or seeking to cause damage to the environment or to public or private installations or property or to occupying or seizing them, or seeking to jeopardize a national resources.
Council of Arab Ministers of the Interior and Justice, 1998
Sources:The Terrorism Research Center