Definition of terrorism

"Terror" comes from a Latin word meaning "to frighten". The terror cimbricus was a panic and state of emergency in Rome in response to the approach of warriors of the Cimbri tribe in 105BC. The Jacobins cited this precedent when imposing a Reign of Terror during the French Revolution. After the Jacobins lost power, the word "terrorist" became a term of abuse. Although the Reign of Terror was imposed by a government, in modern times "terrorism" usually refers to the killing of innocent people by a private group in such a way as to create a media spectacle. This meaning can be traced back to Sergey Nechayev, who described himself as a "terrorist". Nechayev founded the Russian terrorist group "People's Retribution" (Народная расправа) in 1869.
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).
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.