Terrorism is the systematic application of tactics outside of the recognized rules of warfare and usually on non-combatants, designed to create a state of terror in order to gain a desired goal. The goals vary from group to group and place to place, but are goals the terrorists could not reasonably expect to get through courts of law or in conventional or guerrilla warfare. In the case of Islamic terrorists the goal is to terrorize non-Muslims or different sects of Muslims into yielding territory, adopting Islamic customs or Sharia law, simply not fighting back, or making peace on terms favorable to the terrorists. Methods vary also, but include striking with methods and at targets not allowable under recognized rules of warfare, especially at unarmed civilians and most especially at women and children, and in places that a substantial number of non-combatants could reasonably see themselves being. For example, killing ten people in a subway station produces a lot more terror than killing ten people at isolated fire watch towers.
In the case of Hasan, he planned his attack not on armed soldiers, but where he knew soldiers, dependents and civilians would be unarmed and unprotected. Most soldiers deploying to Afghanistan and Iraq deploy unarmed through Fort Hood, and many of their dependents will be there or at other military bases. People hearing about the terrorism will viscerally feel threatened in their workplace, where weapons are typically not carried and often not allowed. His victims included at least three murdered women, one of them a pregnant twenty-one year old bomb squad technician. Targeting unarmed women causes even more disgust and terror (in Western cultures I mean) than shooting unarmed men. (Seriously, what sort of evil pig shoots unarmed pregnant women?) Targeting unarmed people and especially women is thus a common denominator in Islamic terror attacks, whether against non-Muslims, other Muslim sects, moderate Muslims, or simply anyone who is handy. For example, blowing up a market and killing dozens of women shopping for food has zero military value but great terror value, whereas ambushing a military convoy has military value but little terror value.
In addition, Hasan did his shooting while yelling "allahu akbar" (according to bystanders), another typical trait of Muslim terrorists. And of course his aims are clear from his earlier words - to wound the American military machine and the American nation, and thereby to discourage the War of Terror because in this case the terrorists targeted are Muslim.
Again, I'm guessing by what we know of his own words, but I think I'm safe in saying that if the War of Terror had been against Basque separatists or Irish nationalists or Ulstermen, Hasan would have had no problems with it. That's conjecture, but it's supported by what we have seen and heard of his words and actions. These reasons are why I think this qualifies as terrorism - it was a cold-blooded, calculated attack on unarmed men and women designed to kill as many as possible not because it would have any military value - it obviously didn't - but to produce terror.
Non-Islamic cases of terrorism are rare at the moment, but include Irish nationalists and Ulstermen blowing up each others' pubs, Basque separatists blowing up train stations, Jewish nationalists shooting Palestinian villagers, white separatist and anarchist Timothy McVeigh blowing up the Oklahoma City Federal Building, and anti-abortionists shooting abortion doctors and into abortion clinics. In each case the military or direct value of the action was limited, but the terror produced was considerable and designed to produce a larger indirect effect by terrorizing people - just as Hasan's action, while having no measurable direct impact on the War of Terror, was designed to terrorize those fighting and supporting it. Or to put it another way - you don't yell "Allahu akbar" and shoot dozens of people because your Cheese of the Month is late.
That work for you sport?
Fear my mighty wall of text! Feel its wrath!
Or not, either works for me.