The two names, "oral herpes" and "genital herpes" are actually referring to two different strains of the herpes virus, HSV-1 and HSV-2 correspondently. While both of them are extremely similar in what symptoms they present and how they progress, HSV-1, or "oral herpes", has a preference towards the mouth area and HSV-2 or "genital herpes" has a preference towards the genital area.

Other than that, the only difference is that usually the HSV-2 or "genital herpes" is more aggressive and cause both more and worse outbreaks than the former type.

Another piece of fun fact is that having one strain of the virus usually gives you an increased protection from getting the other type.