Terrorists define themselves as freedom fighters, and the general public defines freedom fighters as terrorists.
Can't anyone be a freedom fighter, no matter what there cause is? Lets say New York suddenly decided it didn't like the government, formed a militia, and raged through New Jersey burning and shooting people. Would seem like a group of crazy terrorists, correct? But they are fighting for a certain freedom, lets say they want to secede from the government, so that would make them freedom fighters. I think a terrorist would someone who is mentally ill and goes on rampages killing people because he causes terror and has no motive for doing so, or someone who just generally likes killing/hurting/blowing things up. 9/11 is defined as a terrorist act, but the men who did it believed they were doing it for a just cause, so they would be considered freedom fighters.