The meaning of ‘terrorism’

US Law:

… premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents

Department of Defense:

The calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.

FBI:

The unlawful use of force or violence against persons or property to intimidate or coerce a Government, the civilian population, or any segment thereof, in furtherance of political or social objectives.