Terrorism is, in its broadest sense, the use of intentionally indiscriminate violence as a means to create terror or fear, in order to achieve a political, religious, or ideological aim. It is classified as fourth-generation warfare and as a violent crime. In modern times, terrorism is considered a major threat to society and therefore illegal under anti-terrorism laws in most jurisdictions. It is also considered a war crime under the laws of war when used to target non-combatants, such as civilians, neutral military personnel, or enemy prisoners of war.
A broad array of political organizations have practiced terrorism to further their objectives. It has been practiced by both right-wing and left-wing political organizations, nationalist groups, religious groups, revolutionaries, and ruling governments. It has been argued that terrorism is particularly effective against democracies because the electorate typically is highly sensitive to civilian casualties from terrorist acts, which induces its leaders to grant concessions to terrorist factions. Authoritarian regimes, in contrast, are responsive only to the prefaces of the ruling elite, and therefore are less likely to accede to terrorist demands in response to civilian casualties.The symbolism of terrorism can exploit human fear to help achieve these goals. There is no universally agreed upon definition of the term, and many definitions exist.
According to data from the Global Terrorism Database, more than 61,000 incidents of non-state terrorism, claiming over 140,000 lives, have been recorded from 2000 to 2014.