The day before Obama on his 9-11-01 anniversary speech used the term an act of terrorism.
http://www.cbsnews.com/8301-503544_162-57510394-503544/obama-romney-mark-9-11-anniversary-/
the president said. “No single event can ever destroy who we are. No act of terrorism can ever change what we stand for.”
An act of terror is not the same as an act of terrorisim.
Terror: great fear.
See flyers for Knott’s Berry Farms Halloween fest
Terrorism:
Terrorism is the systematic use of terror, especially as a means of coercion. In the international community, however, terrorism has no legally binding, criminal law definition.[1][2] Common definitions of terrorism refer only to those violent acts which are intended to create fear (terror), are perpetrated for a religious, political or, ideological goal; and deliberately target or disregard the safety of non-combatants (civilians).