2. The glitched result or area outside of a room where such an act is possible.
The term was first coined to describe the glitched areas of the original Metroid game for NES, caused by leaving rooms in the wrong directions (where no doors existed) and causing the game to load data in an order that was never meant to happen in the normal course of gameplay.
The term was made popular by the discovery of holes in wall collision detection in the Nintendo Gamecube game Metroid Prime, which allowed players to walk around outside loaded rooms, view far-away scenery up close, and experience the unique physics and glitches of such an act.
Although the term Secret World is used mainly in the context of Metroid games, it is often applied to any game where the opportuntiy to escape clipping exists.