[Airbornelawyer]

From a June 2003 Army TSP on "Paramilitary and Nonmilitary Organizations and Tactics":

Insurgent forces are groups that conduct irregular or unconventional warfare within the borders of their country in order to undermine or overthrow a constituted government or civil authority. The distinction between terrorists and insurgents is often blurred because of the tactics employed by each. Some terrorists groups have become insurgent organizations, while insurgent organizations have used terror tactics. An insurgent organization may use more than one form of tactics and, based on its strategy, its actions could cut across the entire spectrum of warfare - employing terror, guerrilla, and conventional military tactics to achieve its goals. Typically, most insurgent groups use the first two.