Definitions of terrorism are enormously popular. Google says that terrorism is defined by the US Department of Defense as:
"the unlawful use of -- or threatened use of -- force or
violence against individuals or property to coerce or
intimidate governments or societies, often to achieve
political, religious, or ideological objectives."
The "unlawful" term means that acts of war may not be "terrorism", and the various definitional fights at the United Nations, on the Web and in various agencies are each an effort to paint specific groups either as "terrorists" or "not terrorists".
My definition of terrorism would focus on the target not the actor. Terrorism could be defined as an act of mass violence or intimidation by states or non-state actors against civilians for the purpose of depriving the victims of the will to fight back as opposed to depriving the victim of the means to fight back. Attacks by states or non-state actors against military, governmental or significant economic targets are acts of war not terrorism.
The reason for a definition is to see who is included and who is excluded in the definitions. The primary inclusion in the world overall are the Palestinians who have largely invented modern terrorism. Palestinian targets are almost exclusively civilians with a particular targeting of children and other non-military and non-economic "soft" targets. Palestinians have invented a modern cult of child sacrifice, using their own children as human bombs to kill Jewish children, and they have infused their culture with the death-worship and glorification of murder. By monetary rewards to killers, cultural glorification of anti-Semitism, and the promotion of the cult of death, Palestinians are archetypical terrorists under my definition.
The reason to include governments is that some acts of war serve the same purpose. The German Blitz of 1940 against London is an example in which the targets were not chosen for military value and were intended, unsuccessfully, to defeat the British will to fight. A somewhat more successful model was the American atomic bombing of Hiroshima and Nagasaki, neither of which had significant military value, both of which targeted predominantly or exclusively civilian targets and which had the intent and effect of breaking the Japanese will to fight as opposed to their means to fight. Those nuclear attacks and the February 1945 firebombing of Dresden were terrorist attacks in my judgment.
I am interested that under my definition Al Quaeda is not a terrorist organization. Al Quaeda attached Marines in Lebanon, U.S. embassies in Africa and the USS Cole, all, it seems to me to bear more the hallmarks of war than terrorism. And, the September 11 attacks were directed to the Pentagon, a purely military target, the World Trade Center, an economic target and most likely the White House for Flight 93. I do not believe the September 11 attacks were intended to intimidate America. I believe they should more correctly be seen as acts of war striking at specific military, economic and political targets well within the usual definitions of war.
While it may suit the politicians to paint Bin Laden as a "terrorist", he is not so in my mind. Rather, unlike the Palestinians who would not attack anyone who could fight back, Bin Laden is an Islamic fascist warrior bringing the battle to his enemy’s strengths.
It is not clear to me that this, or any other definition is particularly useful, but it does point out to me the difference between acts of war and acts of terror.