The role playing game is another loose term much like how video game is a loose term. Basically the role playing game or RPG, is a game in which the user assumes a role and plays through the game as that character. It is almost like reading a story from a first person point of view, except for the fact that in RPGs or any video game for that matter, the user of the game is in control, and has the ability to make decisions of what to do in the game world.
In many role playing games there is a set objective or goal, for example "save the princess," or "defeat the evil that haunts the land." In most of these games, there is also combat, and an inventory / item system. The items that a user may posses in this type of video game usually serve a purpose, and sometimes act as key-items that may allow the user to open a door into a new area for example. Some examples of the RPG are the Legend of Zelda series, Zork, and even independant games like Cave Story.
The RPG has evolved over time from the text based games like Zork, to the newest 3d environment games such as Legend of Zelda for the Nintendo Wii. The difference, between these games is usually in the game play, and how they're written. If the screen can display a picture of the world, then there doesn't need to be narration that states what the environment looks like.
The RPG has its roots in the table-top RPG. The most well known example of such a game is Dungeons and Dragons. Since then, RPG games can be about many things, and are sometimes classified as interactive fictions.
Most notable about the RPG in general is the definite amount of control the user has in the story telling of such a game. The user normally completes events in the game in some sort of path, even if that path is just one of exploration around the virtual world. In Hypertext systems a user will also follow a path. This path is created by following links on hypertext documents.