Terrorism is defined, at its simplest, as: any act designed to cause terror. Despite its name, not all actions that are terrifying or terrible are described as terrorism. There is no universal consensus as to what is or is not included, but terrorism is generally understood to feature a political objective, whether that means the politics of nationalism, ethnicity, religion, ideology or social class, amongst others. Definitions as to which acts of violence are considered terrorism will be more often subjective than objective. Since the terrorist act is the symptom of a struggle that has a national, religious or social cause, then the response to it is also often determined by ethnicity, beliefs or class. Furthermore, since attitudes to nationalism, religion, and social status tend to evolve over the course of time, it follows that acts of terrorism, and the individuals or organisations engaging in that terrorism, may - and often are - re-examined retrospectively, being either legitimised or criminalised according to the subsequent prevailing political perspectives.
The Global Terrorism Database (GTD) is a database of incidents of terrorism from 1970 onward. The database is maintained by the National Consortium for the Study of Terrorism and Responses to Terrorism (START) at the University of Maryland, College Park in the United States.