In many countries, acts of terrorism are legally distinguished from criminal acts done for other purposes, and "terrorism" is defined by statute; see definition of terrorism for particular definitions. Common principles among legal definitions of terrorism provide an emerging consensus as to meaning and also foster cooperation between law enforcement personnel in different countries. Among these definitions there are several that do not recognize the possibility of legitimate use of violence by civilians against an invader in an occupied country and would, thus label all resistance movements as terrorist groups. Others make a distinction between lawful and unlawful use of violence. Ultimately, the distinction is a political judgment. In November 2004, a United Nations Security Council 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." (Note that this report does not constitute international law.) U.S. Department of Defense (DoD) defined terrorism as: “The calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.” 
Official definitions determine counter-terrorism policy and are often developed to serve it. Most government definitions outline the following key criteria: target, objective, motive, perpetrator, and legitimacy or legality of the act. Terrorism is also often recognizable by a following statement from the perpetrators.
Violence – According to Walter Laqueur of the Center for Strategic and International Studies, "the only general characteristic of terrorism generally agreed upon is that terrorism involves violence and the threat of violence." However,...