This is my simplest and most honest answer to the question in the page's title. People who already know what an RPG is - I mean really, is there anyone under 35 who hasn't grown up playing computer games? - will recognize the idea, but be enlightened by the face-to-face manner of execution. You will note that "role-playing," "story-telling," "personas" and the like are left behind with the excess baggage. And heretically, I address the question of winning. For this game eventually will come with training wheels, a model starter Generick Fantasye dungeon, village and town which the uncreative GM will learn from, and the creative GM will need no instruction to supersede.
The list of options in the lower right owes some debt to a number of posts over the past half year or so, in the Hack and Slash blog.