Role Playing Game(RPG) is a game categoly. It needs rulebook(and some charts), pencils, papers, dies and some players. One of the players became game-master(or judge, refly and so on) and control the play. Easch player controls a character lives in fictional world like science fiction, fantasy and horrors. These characters have their own abilities and limits. The game-master create situations as chalenge(scenario) and players decide how their characters act.
RPG rulebook provide informations about the fictional world where characters live. They are temporal common sence in the play. Some RPG use popular fictions as its world. (StarWars, Middle Earth, Cthuluhu...)
RPG is a hobby to realize joining someone into fictions...