"You are now standing in an ancient ruin. Behind the crumbling stones of a ruined temple, you can see a dark corridor leading deep into the earth. Inside may be hidden treasures, but dangerous monsters may also be lying in wait. What will you do?"
A Role Playing Game (hereafter abbreviated as "RPG" below) is, as the name suggests, a type of game in which you take on the role of character (as in a play), and act according to a certain set of rules.
If you take the events of this game, and connect them one-by-one, they can be read as a complete adventure novel.
This why RPGs are sometimes also referred to in Japan as interactive fiction, or "novels written on the computer."
Of course, you are the main character, and it is you who guides this story!