Curious To Know How You All................?

Would define a "terrorist"? I'm just asking because you hear that word in the media, and in conversations on a daily basis. I know what the people that we've labeled as terrorist are...such as those in Syria or Iraq. However, what about the people in some countries that have recently, or in history, fought against their government or attempted to overthrow their government, or get rid of their President or ruler....I believe they sometimes refer to them as "rebels"? Would they be considered terrorists as well? Are rebels the same thing as terrorists?