An invisible wall (or alpha wall) is a boundary in a video game that limits where a player character can go in a certain area, but does not appear as a physical obstacle.[1] The term can also refer to an obstacle that in reality could easily be bypassed, such as a mid-sized rock or short fence, which does not allow the character to jump over it within the context of the game.[2] In 2D games, the edge of the screen itself can form an invisible wall, since a player character may be prevented from traveling off the edge of the screen. [citation needed]
In 3D games, invisible walls are used similarly to prevent a player leaving the gameplay area, or getting trapped in a small inescapable space, though visible boundaries such as stone walls or fences are generally preferred. Completely invisible walls are cited to be level design bugs, and might be "left-over geometry" from an earlier version of the level or an object's improperly-aligned collision box.[3][4] Nevertheless, designers might add invisible walls on cliffs to keep characters from falling off[5] or use them as final borders of large open worlds, to make the world appear even larger than it actually is.[3]