The word "terrorism" is politically and emotionally charged, and this greatly compounds the difficulty of providing a precise definition. Studies have found over 100 definitions of “terrorism”. The concept of terrorism may itself be controversial as it is often used by state authorities (and individuals with access to state support) to delegitimize political or other opponents, and potentially legitimize the state's own use of armed force against opponents (such use of force may itself be described as "terror" by opponents of the state).
Terrorism has been practiced by a broad array of political organizations for furthering their objectives. It has been practiced by both right-wing and left-wing political parties, nationalistic groups, religious groups, revolutionaries, and ruling governments. An abiding characteristic is the indiscriminate use of violence against noncombatants for the purpose of gaining publicity for a group, cause, or individual. The symbolism of terrorism can leverage human fear to help achieve these goals.