Definitions for wallhack
A patch enabling a player to cheat by modifying the properties of walls, as by making them transparent or nonsolid.
The New Hacker's Dictionary
A form of game cheat especially associated with first-person shooters like Quake, in which the walls in the simulated maze or dungeon are rendered transparent to the cheater. This gives the cheater normally hidden information about the whereabouts of other players. Beyond gaming, a wallhack is the paradigm case of a whole class of security problems that stem from the fact that a server cannot trust client software, and server authors must assume that all computation farmed out to a client is exposed to and can be interfered with by the user.