From FBI link: In using the term Domestic Terrorism, DHS looks to the Homeland Security Act definition of terrorism, 6 U.S.C. 101(18), which is substantially similar but not identical to the title 18 definition. That provision defines terrorism as any activity that:

• Involves an act that: o Is dangerous to human life or potentially destructive of critical infrastructure or key resources; and o Is a violation of the criminal laws of the United States or of any State or other subdivision of the United States; and • Appears to be intended: o To intimidate or coerce a civilian population; o To influence the policy of a government by intimidation or coercion; or o To affect the conduct of a government by mass destruction, assassination, or kidnapping.