Then how is it determined? There are different possible definitions, as this term is subjective, just like "terrorist".
In correct usage, they are not subjective, bub. To be a freedom fighter, you must fight for freedom. To be a terrorist, you must purposely target civilians.
Even if I incorrectly label a group that targets civilians as "freedom fighters", if they are not fighting for freedom, that label is incorrect.
Let's use an example: A group lives in a society where they enjoy many things that we label as basic freedoms, but they choose not to partake of many of these freedoms. Now, this group does not like that other people can engage in these freedoms and it is their desire to live in a society where basic freedoms are denied to the people.
They take up armed conflict against the rulers of this society.
They cannot be correctly labelled "freedom fighters" because it is their desire to eliminate the freedom which already extant, and replace it with oppression.
Now let's say that they do not target civilians. In fact they take pains to prevent civilian casualties. Then they ALSO cannot be labelled "terrorists", because they do not engage in terrorism.
In this case, the only names that could apply that would be accurate would be "Rebels", "Insurgents", "Dissidents", "Paramilitary group" etc.
Conversely, lets say there is a group that lives in an oppresive society. They choose to take up arms in order to overthrow this oppresive regime and instill a free society. They can correctly be labelled "freedom fighters".
But let's say that this particular group purposely targets civilians in order to achieve their goals. Then they would
also be terrorists.
One can be both freedom fighter and terrorist.
One label is regarding WHAT they are fighting for, the other is regarding HOW they go about fighting for it.