The term "terrorism" is usually taken to mean an attack on civilians, though as a legal matter, this is far from settled. This definition would exclude the Fort Hood shooting, where the targets were soldiers. In any case, the bet is over non-state, politically motivated killing, which is broader and would include Fort Hood, I think.
I would like to propose this as a thread for people to write in their predictions for the next year and the next decade, when practical with probabilities attached. I'll probably make some in the comments.