By their fruits...

On the definition of terrorism, the UK Guardian had a helpful piece ages ago—ironically published about 4 months prior to 9/11 (just avoid the Leftish assumptions the writer slips in here and there)—analyzing the official US definition put out by the State Department:

“Premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents, usually intended to influence an audience.”

However, the State Department adds qualifiers to clarify what is meant by “noncombatants”:

The state department regards attacks against “noncombatant* targets” as terrorism. But follow the asterisk to the small print and you find that “noncombatants” includes both civilians and military personnel who are unarmed or off duty at the time. Several examples are given, such as the 1986 disco bombing in Berlin, which killed two servicemen.
The most lethal bombing in the Middle East last year was the suicide attack on USS Cole in Aden harbour which killed 17 American sailors and injured 39 more.
As the ship was armed and its crew on duty at the time, why is this classified as terrorism? Look again at the small print, which adds: “We also consider as acts of terrorism attacks on military installations or on armed military personnel when a state of military hostilities does not exist at the site, such as bombings against US bases.”

The slaughter at Fort Hood in late 2009, for example, was terrorism under this definition (and certainly not the laughable "workplace violence" President Obama has seen fit to label it).  Calling it “terrorism”, however, is a bit too general.  It's like calling an orange “a plant”—when it’s more pertinent to call an orange “a citrus fruit”.  That one-man commando operation by (American Muslim Major and Army Psychiatrist in the U.S. Army) Nidal Malik Hasan, then, was more specifically a razzia—itself a subcategory of qital—the violent form of Jihad (e.g., in its imperative form qatiloo in verse 9:29 of the Koran, properly translated as "Kill", though too often softened as "Fight")—i.e., the war which Muslims have been waging against the West unremittingly for 1,400 years, never ceasing, only either pretending to cease or taking a break due to circumstances of weakness, and now being renewed with escalating vigor in a global revival of Islam.

It’s not apples and oranges: By their fruits ye shall know them.