Terrorism is, in the broadest sense, the use of intentionally indiscriminate violence as a means to create terror among masses of people; or fear to achieve a financial, political, religious or ideological aim.^[1] It is used in this regard primarily to refer to violence against peacetime targets or in war against non-combatants.^[2] The terms "terrorist" and "terrorism" originated during the French Revolution of the late 18th century^[3] but gained mainstream popularity during the U.S. Presidency of Ronald Reagan (1981–89) after the 1983 Beirut barracks bombings^[4] and again after the attacks on New York City and Washington, D.C. in September 2001^[5][4][6] and on Bali in October 2002.^[4]

There is no commonly accepted definition of "terrorism".^[7][8] Being a charged term, with the connotation of something "morally wrong", it is often used, both by governments and non-state groups, to abuse or denounce opposing groups.^{[9][10][4][11][8]} Broad categories of political organisations have been claimed to have been involved in terrorism to further their objectives, including right-wing and left-wing political organisations, nationalist groups, religious groups, revolutionaries and ruling governments.^[12]Terrorism-related legislation has been adopted in various states, regarding "terrorism" as a crime.^[13][14] There is no universal agreement as to whether or not "terrorism", in some definition, should be regarded as a war crime.^[14][15]

According to the Global Terrorism Database by the University of Maryland, College Park, more than 61,000 incidents of non-state terrorism, resulting in at least 140,000 deaths, have been recorded from 2000 to 2014.^[16]