There is no consensus as to whether terrorism should be regarded as a war crime.The Global Terrorism Database, maintained by the University of Maryland, College Park, has recorded more than 61,000 incidents of non-state terrorism, resulting in at least 140,000 deaths, between 2000 and 2014. Etymology
Etymologically, the word terror is derived from the Latin verb Tersere, which later becomes Terrere. The latter form appears in European languages as early as the 12th century; its first known use in French is the word terrible in 1160. By 1356 the word terreur is in use. Terreur is the origin of the Middle English term terrour, which later becomes the modern word "terror". Historical background
The term terroriste, meaning "terrorist", is first used in 1794 by the French philosopher François-Noël Babeuf, who denounces Maximilien Robespierres Jacobin regime as a dictatorship. In the years leading up to what became known as the Reign of Terror, the Brunswick Manifesto threatened Paris with an "exemplary, never to be forgotten vengeance: the city would be subjected to military punishment and total destruction" if the royal family was harmed, but this only increased the Revolutions will to abolish the monarchy. Some writers attitudes about French Revolution grew less favorable after the French monarchy was abolished in 1792.
It is common for both parties in a conflict to describe each other as terrorists.On whether particular terrorist acts, such as killing non-combatants, can be justified as the lesser evil in a particular circumstance, philosophers have expressed different views: while, according to David Rodin, utilitarian philosophers can (in theory) conceive of cases in which the evil of terrorism is outweighed by the good that could not be achieved in a less morally costly way, in practice the "harmful effects of undermining the convention of non-combatant immunity is thought to outweigh the goods that may be achieved by particular acts of terrorism". Among the non-utilitarian philosophers, Michael Walzer argued that terrorism can be morally justified in only one specific case: when "a nation or community faces the extreme threat of complete destruction and the only way it can preserve itself is by intentionally targeting non-combatants,then it is morally entitled to do so".In his book Inside Terrorism Bruce Hoffman offered an explanation of why the term terrorism becomes distorted:

On one point, at least, everyone agrees: terrorism is a pejorative term. It is a word with intrinsically negative connotations that is generally applied to ones enemies and opponents, or to those with whom one disagrees and would otherwise prefer to ignore. What is called terrorism, Brian Jenkins has written, thus seems to depend on ones point of view.