'terrorist' has a fairly specific meaning: not just a rebel or an insurgent but someone who carries out acts against innocent people to try to force government action. (You could be a rebel who doesn't take terrorist actions.) This has changed since the French revolution, when the 'terrorists' were the government acting against members of the previous regime.
As for the rest of the words like rebel, insurgent, freedom fighter, resistance - well, history is written by the winners. If you won, you're a freedom fighter, if you lost you're a rebel.
"Treason never prospers - what's the reason?
If it prospers, none dare call it treason."