Supporters of the self-styled "militia" occupying buildings at a high desert wildlife preserve in Oregon have taken great umbrage at the group being called "terrorists." Their objection rests largely on the claim that these people have not destroyed property or hurt anyone. This argument misses the point, but it does highlight the importance of defining terms, especially those applied to such a complex, diverse phenomenon. People may be surprised to learn that there is no agreed upon definition of terrorism. Different U.S. agencies define it differently, and the UN has yet to agree on what the word means. Among those who study this phenomenon there is, however, a broad consensus on the characteristics of terrorism. Sometimes a functional definition works better than an academic one. You don't need a biological definition of an elephant to recognize one when you see it.
The Department of Defense Dictionary of Military and Related Terms provides a useful place to start discussion of this topic. It defines terrorism as "The unlawful use of violence or threat of violence, often motivated by religious, political, or other ideological beliefs, to instill fear and coerce governments or societies in pursuit of goals that are usually political." Violence, illegality, and ideology form the unholy trinity at the core of all terrorist groups. By this definition it is hard to see how the Oregon standoff is anything but terrorism. A group of heavily armed men motivated by anti-government ideology and with no legal authority have occupied Federal property and are threatening to resist with deadly force any effort by law enforcement to remove them. They seek to force the government to turn the land over to the people they claim to represent. Their action thus has all the characteristics named in the DOD definition.
I have a strong suspicion, though, that objections to the terrorist label are more visceral. Terrorists are supposed to be dark-skinned and non-Christian. People are thus quick to apply the term to outsiders and far more willing to find a gentler word to describe those from their own social group. If members of the Black Lives Matter or Occupy Wall Street movements had shown up to their protests as heavily armed as the men in Oregon, the same people defending the "militiamen" would probably be calling on the government to use all necessary force to apprehend the "terrorists."