An Officer is a high-ranking soldier in any given military faction, allied with either the Imperial Legion or the Stormcloaks. Officers can be distinguished from regular soldiers by their armor, and most distinctively, their helmets.
While they often have special names and wear the officer uniforms of their respective faction, they otherwise usually share identical statistics as their generic soldier counter-types.
Stormcloak officers most often wear a full set of Stormcloak officer armor. They are most often encountered in major city battles as part of the Civil War quest-line, appearing first in the Battle for Whiterun if allied with the Imperial Legion. Many of them are female.