The terms "terrorism" and "terrorist" (someone who engages in terrorism) carry strong negative connotations.[40] These terms are often used as political labels, to condemn violence or the threat of violence by certain actors as immoral, indiscriminate, unjustified or to condemn an entire segment of a population.[41] Those labeled "terrorists" by their opponents rarely identify themselves as such, and typically use other terms or terms specific to their situation, such as separatist, freedom fighter, liberator, revolutionary, vigilante, militant, paramilitary, guerrilla, rebel, patriot, or any similar-meaning word in other languages and cultures. Jihadi, mujaheddin, and fedayeen are similar Arabic words which have entered the English lexicon. It is common for both parties in a conflict to describe each other as terrorists.[42]
On the question of whether particular terrorist acts, such as killing civilians, 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 which 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".[43] 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".[43][44]
http://en.wikipedia.org/wiki/Terrorism