From Noam Chomsky's ZNet Blog
The US Code for defining an "act of terrorism" is an activity that -- (A) involves a violent act or an act dangerous to human life that is a violation of the criminal laws of the United States or any State, or that would be a criminal violation if committed within the jurisdiction of the United States or of any State; and (B) appears to be 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 assassination or kidnapping.
Two points. First, I've been using this and other official US definitions since I began writing on the topic in the early 80s, immediately after the Reaganites declared their war on terror.
For two reasons: (1) they are reasonable and close to common usage, and (2) they are appropriate, because the government that offers these definitions cannot claim that it is exempt from their consequences. Second point is that later this definition has been withdrawn, presumably because it was recognized that an immediate consequence is that the US is a leading terrorist state. Though it is safe to rely on the intellectual class not to draw the conclusion, nevertheless there are always mavericks who tell irritating truths, and sometimes the usual techniques of lying, hysteria, tantrums, etc., do not suffice among the general public, even though they almost invariably do among the educated classes. For that reason, the standard view now is that defining "terrorism" is a profound problem, to be dealt with in international conferences, academic studies, etc. And it's true that it is a very hard problem to define "terrorism" so that it singles out what they do to us and our clients, but excludes what we and our clients do to them -- a problem so far not solved and very profound, no doubt...