There is some legal definition for "terrorism" in german criminal law (do not ask me the details, but there is a difference if an act of murder was a terroristic act or not - it has to do with intentions, means, motives, acting alone or in a network and so on). So there is some factual definition.

A quote like "They call him freedom fighter, I call him terrorist" is clearly an opinion and yes, it makes a difference whether you use the word in the sense of a legal definition or an abstract concept or a hyperbolic metaphor. The level rod is dignity.