Regarding the "kidnapping" versus "capturing" thing, a soldier might be "captured" if they're on the battlefield in some disputed territory. At that point they are usually held prisoner until hostilities end or they are killed if they are particularly unfortunate. They are "kidnapped" when they are taken not in a battle to determine who gets to hold the terrain, but as part of a plan whose sole aim is to retreat with the soldier(s) in custody and then ask for ransom against the threat of killing the captive.

Under the normal rules of war, soldiers are "captured" under two circumstances that I can think of. Either they are taken by force and kept alive because they may know something of value or they have voluntarily surrendered either as an individual or part of a larger, defeated group. There are no usually no "conditions" assigned to their eventual release and certainly no death threats.

On the other hand, I would never call attacks on soldiers "terrorism" as some do. I reserve that for deliberate attacks against targets where the only conceivable casualties are civilians. The attackers may still be "terorrists" though in my opinion if they incorporate attacks on civilians as part of their plan to gain power.