For the purposes of the Geneva Conventions, prisoners are either medical personnel (and I guess chaplains, too), POWs, or civilians. The civilians may be combatants or non-combatants. The reason it is broken down this way is because each of these categories is covered by a different article in the Geneva Conventions. Civilian combatants and non-combatants are both covered by the same article, and it is not the same one as POWs, or medical personnel and chaplains.