Invisible wall

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. 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. 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.

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. Nevertheless, designers might add invisible walls on cliffs to keep characters from falling off or use them as final borders of large open worlds, to make the world appear even larger than it actually is.