Map editing cheat

Map editing is a multiplayer cheat where the levels are altered in order to gain an unfair advantage. Typically, this allows the cheating player to be able to see through walls which normally do not permit player vision, or into areas which normally are blocked by a wall with a solid appearance.

One possible side effect of this cheat may be that in certain instances, the non-cheating player's usage of the "Silent BFG" is fully audible to the cheating player as though it were a normally-fired BFG. In this event, this same characteristic would cause a cheating player to be unable to hear whether his own "Silent BFG" was effective when activated against the wall units which are permitting visibility (although the non-cheating player would hear the sound with the "Silent BFG" effect as long as it was correctly executed by the cheating player). Executions of Silent BFG against unmodified wall tiles within the map would function normally, silencing the BFG in the perspectives of both players.

This cheat takes the form of an altered IWAD file or a PWAD addition used as a replacement for the original map.

Source

This writeup includes text from Map editing cheating in Doom2, used with permission.