The Definition

If war is diplomacy by other means, than an entirely puposive definition of terrorism can't work. If terrorism is just the use of violence to acheive a political end or send a message, then isn't all warfare terrorism? Would we prefer killing for the sole atavistic joy of bloodlust satisfied?

Similarly, tactics common to assymmetric warfare cannot make it terrorism. Guerilla warfare, even suicide bombings, are not per se terrorist, unless you're content to paint every national resistance movement ever with the same brush.

Therefore, it can only be the intentional targetting of non-combatants that makes a terrorist act.