The word terrorism has been defined in many different ways by many different sources, and is therefore a controversial term without a simple agreed meaning.

Criteria

Generally speaking a definition of terrorism should examine each of the four major criteria, which are as follows:

• Target. It is commonly held that the distinctive nature of terrorism lies in its deliberate and specific selection of civilians (or military personnel not on active combat duty) as targets. Furthermore, an act is more likely to be considered terrorism if it targets a general populace than if it purposefully targets a specific individual or group. See also noncombatant and collateral damage.
  • This criterion excludes conventional warfare in accordance with the laws of war, attacks on military targets during time of war, and guerilla warfare and revolution.
• Objective. As the name implies, terrorism is understood as an attempt to provoke fear and intimidation. Hence, terrorist acts are designed to attract wide publicity and cause public shock, outrage and fear. The objective is closely allied to the nature of the target. By deliberately selecting defenceless and unsuspecting civilians as targets, the terrorist ensures that the level of shock and outrage, as well as the publicity, will be extreme. It may also be part of the terrorist's objective to provoke disproportionate reactions from states. For example, some argue that the 9/11 attacks on the World Trade Center in New York were intended to draw the United States into an escalating conflict with Islam worldwide.
  • This criterion excludes the Holocaust and other cases of genocide, which are undertaken to exterminate, not to intimidate, and which are usually hidden rather than publicized. Also, any violence against targets unlikely to attract public notice and having little effect on the populace at large.
• Motive. These acts are intended to achieve political or religious goals, not for personal gain. For example, a gang of bank robbers who kill the bank manager, blow up the vault and escape with the contents would normally not be classed as terrorists, because their motive was profit. However, if a gang were to execute the same assault with the intent of causing a crisis in public confidence in the banking system, followed by a run on the banks and a subsequent destabilization of the economy, then the gang might be classed as terrorists.
  • This criterion excludes organized crime.
• Legitimacy. Some hold that a legitimate government cannot, by definition, commit terrorism on its own territory. In this view, a state can commit war crimes or crimes against humanity, but these actions are distinct from terrorism. See state terrorism.
  • This criterion excludes warfare between states, government repression, the Holocaust and other state-sponsored genocide.

Various definitions

• Academic Consensus: an anxiety-inspiring method of repeated violent action, employed by (semi-) clandestine individual, group or state actors, for idiosyncratic, criminal or political reasons, whereby - in contrast to assassination - the direct targets of violence are not the main targets. The immediate human victims of violence are generally chosen randomly (targets of opportunity) or selectively (representative or symbolic targets) from a target population, and serve as message generators. Threat- and violence-based communication processes between terrorist (organization), (imperilled) victims, and main targets are used to manipulate the main target (audience(s)), turning it into a target of terror, a target of demands, or a target of attention, depending on whether intimidation, coercion, or propaganda is primarily sought
• Noam Chomsky: the calculated use of violence or the threat of violence to attain political or religious ideological goals through intimidation, coercion, or instilling fear. (taken from a US Army manual)
• League of Nations Convention (1937): 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.
• United States Code of Federal Regulations: 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.
• United States Department of Defense: the calculated use of violence or the threat of 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.
• Jason Burke, an expert in radical Islamic activity, has this to say:

"There are multiple ways of defining terrorism, and all are subjective. Most define terrorism as 'the use or threat of serious violence' to advance some kind of 'cause'. Some state clearly the kinds of group ('sub-national', 'non-state') or cause (political, ideological, religious) to which they refer. Others merely rely on the instinct of most people when confronted with an act that involves innocent civilians being killed or mainmed by men armed with explosives, firearms or other weapons. None is satisfactory, and grave problems with the use of the term persist. Terrorism is after all, a tactic. The term 'war on terrorism' is thus effectively nonsensical. As there is no space here to explore this involved and difficult debate, my preference is, on the whole, for the less loaded term 'militancy'. This is not an attempt to condone such actions, merely to analyse them in a clearer way." ("Al Qaeda", ch.2, p.22)

References

• United Nations Office on Drug and Crime (http://www.unodc.org/unodc/terrorism_definitions.html)
• Center for Health Statistics (http://www.cdc.gov/nchs/about/otheract/icd9/appendix1.htm)
• U.S. Government Accountability Office (http://www.gao.gov/atext/d03165.txt)
• Howard Zinn, Terrorism and War, (2002) ISBN 1583224939