What is Terror?

Legal Definition
That state of the mind which arises from the event or phenomenon that may serve as a prognostic of some catastrophe affright from apparent danger.

2. One of the constituents of the offence of riot is that the acts of the persons engaged in it should be to the terror of the people, as a show of arms, threatening speeches, or turbulent gestures; but it is not requisite, in order to constitute this crime, that personal violence should be committed. 3 Camp. R. 369; 1 Hawk. P. C. c. 65, s. 5; 4 C. & P. 373. S. C. 19 E. C. L. R. 425 4 C. & P. 538; S. C. 19 E. C. L. R. 616. Vide Rolle's R. 109; Dalt. Just. c. 186; 19 Vin. Ab. Riots, A 8.

3. To constitute a forcible entry, 1 Russ. Cr. 287, the act must be accom-panied with circumstances of violence or terror; and in order to make the crime of robbery, there must be violence or putting in fear, but both these circumstances need not concur. 4 Binn. R. 379. Vide Riot; Robbery; Putting in fear.
-- Bouviers Law Dictionary
Legal Definition
Alarm; fright; dread; the state of mind induced by the apprehension of hurt from some hostile or threatening event or manifestation; fear caused by the appearance of danger. In an indictment for riot, it must be charged that the acts done were "to the terror of the people." See Arto v. State, 19 Tex. App. 136.
-- Black's Law Dictionary