It often seems to be the case that one man's terrorist is another man's freedom fighter. In the complex world in which we live it can be very difficult to establish precisely who are the good guys and who are the bad guys, so to speak.
If we define a terrorist as someone who uses terror to achieve their political objectives then it is often the case that various organizations supported by successive United States governments over the decades—such as the Mujahideen in Afghanistan and the Contras in Nicaragua—fall into this category.
Such organizations were regarded by the relevant US administrations as freedom fighters, risking their lives for a noble cause. (In both cases, the cause was anti-Communism.) But opponents of these groups saw them as terrorists, pure and simple, and condemned them in the same kind of language reserved today for the likes of ISIS and Al-Qaeda.
To a large extent, this is a political question, which like all such questions, doesn't have a simple answer. But in purely factual terms, it does appear to be the case that whether a particular group is to be accounted terrorists or freedom fighters depends on the perspective of those evaluating the individual situation. And such evaluation depends on a large number of relevant factors, mainly those relating to national security.
That's not to say that some groups—such as ISIS, for example—are more difficult to fit into the category of "freedom fighters" than others, but in the final analysis it's not precise definitions that matter in such cases, but the hard-nosed realities of international politics.