Terror" comes from a Latin terrere meaning "to frighten".[13] The terror cimbricus was a panic and state of emergency in Rome in response to the approach of warriors of the Cimbri tribe in 105 BC. The Jacobins cited this precedent when imposing a Reign of Terror during the French Revolution.[14][15] After the Jacobins lost power, the word "terrorist" became a term of abuse.[8] Although the Reign of Terror was imposed by a government, in modern times "terrorism" usually refers to the killing of innocent people[16] by a private group in such a way as to create a media spectacle.[17] This meaning can be traced back to Sergey Nechayev, who described himself as a "terrorist".[18] Nechayev founded the Russian terrorist group "People's Retribution" (Народная расправа) in 1869.

In November 2004, a United Nations Secretary General report described terrorism as any act "intended to cause death or serious bodily harm to civilians or non-combatants with the purpose of intimidating a population or compelling a government or an international organization to do or abstain from doing any act". .[19]

Main article: Definition of terrorism
The definition of terrorism has proved controversial. Various legal systems and government agencies use different definitions of terrorism in their national legislation. Moreover, the International community has been slow to formulate a universally agreed, legally binding definition of this crime. These difficulties arise from the fact that the term "terrorism" is politically and emotionally charged.[20] In this regard, Angus Martyn, briefing the Australian Parliament, stated that "The international community has never succeeded in developing an accepted comprehensive definition of terrorism. During the 1970s and 1980s, the United Nations attempts to define the term foundered mainly due to differences of opinion between various members about the use of violence in the context of conflicts over national liberation and...