From the FBI
Definitions of Terrorism in the U.S. Code
From the site:
“Domestic terrorism” means activities with the following three characteristics:
Involve acts dangerous to human life that violate federal or state law;
Appear intended (i) to intimidate or coerce a civilian population; (ii) to influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination. or kidnapping; and
Occur primarily within the territorial jurisdiction of the U.S.