In the broadest sense, terrorism is the use of deliberately indiscriminate violence as a means of terror among people; or fear of religious or political ends. In this regard, it mainly refers to violence in peacetime or in war against non combatants. The terms "terrorism" and "terrorism" originated from the French Revolution in the late 18th century, but after the bombing of the Bennett barracks in 1983, the US President Ronald Reagan (1981-89) in 2001 and the subsequent attacks on September 11, 2001 and the Bali bombing in 2002.

There is no accepted definition of "terrorism". As a term with the meaning of accusation, it has the meaning of "moral error", which is often used by governments and non-state groups to abuse or condemn opposing groups. It is said that various political organizations are involved in terrorism in order to achieve its objectives, including right-wing and left-wing political organizations, nationalist groups, religious groups, revolutionaries and the ruling government. Each state has passed legislation relating to terrorism, criminalizing "terrorism". There is no general consensus on whether "terrorism" should be considered a war crime in a certain definition.

According to the University of Maryland College Park's global terrorism database, more than 61000 non state terrorism incidents were recorded between 2000 and 2014, resulting in at least 140000 deaths.

Etymologically, the word terror comes from the Latin verb tersere, which later became terrere. The latter form appeared as early as the 12th century in European languages. Its first known usage in French was the dreadful word of 1160. By 1356, the term began to be used. Terreur is the origin of the medieval English term terror, which later became the modern word terror.

There are more than 109 different definitions of terrorism. American political philosopher Michael Walzer wrote in 2002 that "terrorism is the intentional killing of innocent people in order to spread fear among the whole people and force the hands of their political leaders". According to Bruce Hoffman, an American scholar,

A single definition of terrorism cannot be agreed on only in a single agency within the same government agency. Experts in this field and other scholars with a long history are also unable to reach a consensus.

C. The question of how to define terrorism, wrote A.J. Coady, "cannot be solved" because "the natural origin of terrorism is in the context of debate, ideology and propaganda.".

Sophie wahnich, a French historian, distinguished the revolutionary terror of the French Revolution from the terrorists who attacked on September 11:

Revolutionary terror is not terrorism. Achieving moral equivalence between the second year of the revolution and September 2001 is historical and philosophical nonsense The violence of 11 September 2001 was neither equal nor free. Nor did the president of the United States declare war prevention.

Experts disagree that "terrorism is wrong in definition or in fact; they disagree that terrorism should be based on purpose, method, or both; or, should states disagree? Terrorism can be committed; they do not even agree with the importance of terrorism in defining it. "