In my mind a terrorist is a person who creates havoc and death to further their cause. A terrorist is also indescriminate in that they kill both civilians and government/military/religious targets. the difference between a freedom fighter (or other word) and the terrorist is that a terrorist purposefully kills innocents and civilians.
If a group kills govt and military targets that is part of the "war" that they are fighting for and a goal in winning. killing civilians is more about hate than justice. Terrorism is the ultimate hate crime.
