Terrorism has plagued humanity for centuries; some scholars trace its history as far back as the ancient world. Particularly since the attacks of September 11, 2001, terrorism has become a major focus of news stories as well as domestic and international policies. You might be surprised to learn, then, that there is no universally accepted definition of terrorism. In fact, the distinguished scholar Walter Laqueur claims that more than 100 definitions exist. He further contends: “No all-embracing definition will ever be found for the simple reason that there is not one terrorism, but there have been many terrorisms, greatly differing in time and space, in motivation, and in manifestations and aims.”
However, although each definition is distinctive in its details, most definitions include certain fundamental elements. A 2004 United Nations report defined terrorism as “any action…that is intended to cause death or serious bodily harm to civilians or non-combatants, when the purpose of such act, by its nature or context, is to intimidate a population or to compel a government or an international organization to do or to abstain from doing any act.” To be categorized as terrorism, then, actions by individuals and groups must involve violence and threats of violence directed against civilian populations to achieve a political purpose. As the word “terror” suggests, the objective is to intimidate people into acting—or not acting—in particular ways.
This basic description clearly applies to the major terrorist attacks in recent history from 9/11 to the 2004 Madrid train bombings to the 2015 shootings in Paris; San Bernadino, California; and the Planned Parenthood clinic in Colorado Springs, Colorado.
The following links will direct you to various definitions of terrorism, including those cited above.
The discussion of terrorism in the Encyclopedia Britannica includes the following observation: "Terrorism has been practiced by political organizations with both rightist and leftist objectives, by nationalistic and religious groups, by revolutionaries, and even by state institutions such as armies, intelligence services, and police."
Significantly, in addition to acts by individuals and groups, this definition includes state terrorism, which involves violence and oppression perpetrated by governments against civilian populations. Prominent examples of state terrorism are Nazi Germany, the Soviet Union under Stalin, the Khmer Rouge in Cambodia (Kampuchea), and the Ugandan regime of Idi Amin. Although some experts question whether governmental actions can be classified as terrorism, this category is included in this guide because the tactics and objectives parallel those of nongovernmental entities.