Primarily it is the distance at which parallax is corrected. The shotgun scopes also "usually" have more coarse cross hairs. Shotgun scopes I believe are usually corrected for parallax at about 50 yards as compared to about 150 for rifle scopes. This can vary some by manufacturer.
GB hit it on the head with the parallax. Really, parallax won't make a difference, unless you are doing high precision shooting. For deer sized game, you could use a 'shotgun' scope on a rifle, or vise versa without no noticeable difference in a hunting situation.
A forum community dedicated to the great outdoors and hunting enthusiasts. Come join the discussion about hunting, fishing, survival, archery gunsmithing, optics, reviews, accessories, classifieds, and more!