Breaking Oregon Militia Occupies Federal Building

[Oberon]

The first definition on Google gives me:

terrorism
ˈtɛrərɪzəm/
noun
noun: terrorism
the unofficial or unauthorized use of violence and intimidation in the pursuit of political aims.

Now, the Bundy bunch haven't used violence...yet...but by carrying firearms into a federal office and occupying it, one could definitely make the argument that they are using intimidation. In fact if you were to ask them if they wanted to intimidate the federal government they would probably reply in the affirmative.
Are their aims political? Definitely.
Therefore one could make the arguement that they are unofficially using intimidation in the pursuit of a political aim.

Honestly though, right now, I would probably withdraw the claim of terrorism, but it is very close to it. If one of those men fires on an American federal agent then it becomes a 'federal crime of terrorism' under the definition of 18 U.S.C. § 2332b:

Is calculated to influence or affect the conduct of government by intimidation or coercion, or to retaliate against government conduct; and

Is a violation of one of several listed statutes, including § 930(c) (relating to killing or attempted killing during an attack on a federal facility with a dangerous weapon); and § 1114 (relating to killing or attempted killing of officers and employees of the U.S.).

What they are guilty of, at the moment, as per US code 2384 is seditious conspiracy, or:

If two or more persons in any State or Territory, or in any place subject to the jurisdiction of the United States, conspire to overthrow, put down, or to destroy by force the Government of the United States, or to levy war against them, or to oppose by force the authority thereof, or by force to prevent, hinder, or delay the execution of any law of the United States, or by force to seize, take, or possess any property of the United States contrary to the authority thereof, they shall each be fined under this title or imprisoned not more than twenty years, or both.

Either which way it was a stupid move, but Bundys group are rather...zealous in their beliefs and they've been given a lot of leeway by US authorities, some might say too much leeway.