A role-playing game is a computer game genre based on pen-and-paper games such as Dungeons and Dragons.
The original RPG genre was notable in that it evolved from wargames, evolving rules for the progression of "heroes" from battle to battle. A generic fantasy setting was added after rules were devised for miniatures of different scale: smaller ones became hobbits, mid-sized figures represented humans, and larger ones were giants.
Eventually the wargaming aspect faded into the background and the games became about taking on the role of the heroes, hence role-playing game.
Interestingly enough, the computer game counterparts approached this from nearly the opposite direction, where a computer RPG is largely determined to be a game which has many detailed statistics about a character's abilities and skills, often of a multitude of races and/or classes.
The Quest for Glory series allows players to take on the role of a human Hero, playing a fighter, thief, magic-user or (later) a paladin. Points are assigned to abilities and skills at the beginning of each game and increase through use. Like the early RPGs, this hero is able to be re-introduced in successive games in the series, with all his collected experience.