Terrorism is a tactic, employed by a wide array of actors. There is no single creed, ethnicity, political persuasion or nationality with a monopoly on terrorism. Individuals and groups of individuals from almost every conceivable background, from late Victorian-era anarchists to Klansmen to North Korean intelligence officers, have conducted terrorist attacks. Because of the impreciseness of the term, we should not refer to individuals as terrorists. In addition to being a poor descriptor, "terrorist" tends to be a politically loaded term.
Traditionally, terrorism has been a tactic of the weak, i.e., those who lack the power to impose their political will through ordinary political or military means. As Carl von Clausewitz noted, war is the continuation of politics by other means; terrorism is a type of warfare, making it also politics by other means. Because it is a tactic used by the weak, terrorism generally focuses on soft, civilian targets rather than more difficult-to-attack military targets.
The type of weapon used does not define terrorism. For example, using a vehicle-borne improvised explosive device against an International Security Assistance Force firebase in Afghanistan would be considered an act of irregular warfare, but using it in an attack on a hotel in Kabul would be considered an act of terrorism. This means that militant actors can employ conventional warfare tactics, unconventional warfare tactics and terrorism during the same campaign depending on the situation.
Many terrorist acts have a religious element to them, but that element is normally related to a larger, political goal: Both a militant anti-abortion activist seeking to end legalized abortion and a jihadist seeking to end an U.S. military presence may act according to religious principles, but they ultimately are pursuing a political objective.
Geopolitical cycles will change, and these changes may cause a shift in who employs terrorism and how it is employed. But as a tactic, terrorism will continue no matter what the next geopolitical cycle brings.