Can someone explain why the Resistance members are called "rebels"?

I liked TLJ but I was wondering about something and was hoping someone could help me out here.In the OT, they were rebels because they were part of a revolution against the government but in Last Jedi, they are the last remaining leaders of the republic after the first order blew up their home planets right?The first order are kind of like terrorists right? Are they not more like rebels than the heroes? They are now trying to maintain how it was and the First Order is trying to change it. via /r/StarWars https://ift.tt/2F9Ia6f