As the literal meaning of the word indicates, terror is a military strategy that hopes to change the political situation by spreading fear rather than by causing material damage. This strategy is almost always adopted by very weak parties, who are unable to inflict much material damage on their enemies. Of course, every military action spreads fear. But in conventional warfare, fear is a byproduct of material losses, and is usually proportional to the force inflicting the losses. In terrorism, fear is the whole story, and there is an astounding disproportion between the actual strength of the terrorists and the fear they manage to inspire.
-Yuval Noah Harari