HoreTore, here is the definition I found on Wiki:

Terrorism is, most simply, policy intended to intimidate or cause terror. It is more commonly understood as an act which (1) is intended to create fear (terror), (2) is perpetrated for an ideological goal (as opposed to a materialistic goal or a lone attack), and (3) deliberately targets (or disregards the safety of) non-combatants.
An attack by a combatant who is not part of the regular army attacking a force which is essentially trying to be a stabilizing force could be interpreted as 1 or 2.