From Nordic Larp Wiki
A meta room is a space where the players may enrich the stories of the characters beyond the time and space of the "main" larp, and to give players a break and an opportunity to think through their larping without having to go off-game. A meta room might also be used for playing/dancing a symbolic version of something that is meant to be happening in-game, such as two characters fighting or having sex.
The meta room was first introduced in the Swedish Larp En stilla middag med familjen in 2007. This larp used a black box as the meta room, hence the common misunderstanding that a black box and a meta room is the same.
A player may invite any other players to enter the meta room, generally verbally either by asking directly or by using a certain keyword.
To make the usage of the meta room more discrete, some larps have used a meta technique where you hand out an object to invite a co-player, such a feather in Tinget and Just a little lovin' or a political flyer in Red October (all 2011).
Players may normally use the meta room for whatever way they like, but it is often suggested they play out flash-backs (scenes that happened before the larp) or flash-forwards (scenes that may occur in a hypothetical future). In some cases, an organizer might be present in the black box to help players facilitate their scenes and control the sound and lights.
The meta room might also be used with more intricate restrictions on how to use it, for example it may be used to play abstract scenes with voices in a characters head.
Meta room design
The meta room might be a black box with an audio system and adjustable lights, making it easy to change the ambience. This can be help the players adapt emotionally to that their characters are now in a different time or space compared to the "main larp".
However, the meta room might also be just a normal room, with or without light or sound equipment, or even just a designated space outside.