Hall of Mirrors

From Half-Life Library

Hall of Mirrors effect as seen in Action Half-Life 2 from a mapping error

Hall of Mirrors or "HoM" for short, is a mapping error term that effects the GoldSrc engine (Half-Life) as well as the Source engine (Half-Life 2). It occurs when a map is not properly closed off causing the player to "see" outside of the map. It is also commonly seen in many modification's "spectate" mode where you are allowed to exit the map boundaries.

Because the engine doesn't know how to interpret this, it renders frames over top of the previous frame when looking at the hole in the map, much like a "hall of mirrors". It is also commonly used on map reviewing sites to describe mapping flaws within a map. It also exists in a variety of other games and engines including the early Quake engines, the Doom engine and the earlier Unreal engines.