If you are confining gun skills to shooting only, handgun definitiely encompasses pistols (including autopistols) and revolvers. The you have SMGs (including MP5), rifles, shotguns etc.
The skill is primarily used to determine hit probability, in which case the difference between pistols and revolvers is negligable.
The same techniques can be used to shoot all handguns (that use a trigger anyway). The differences lay in maintenance, reloading, cleaning - something not a factor in hit probability.