Some effects target a Game Room. This simply refers to any area that has been defined as a single “room” or “area.” For example, a sleeping cabin or tent is generally a Game Room. Similarly, if you’re using a small clearing on a path to represent a cave during an adventure, the Marshal running the module might say that the clearing counts as a Game Room. It’s also possible for larger areas to be defined as a multiple of several Game Rooms. For example, a tavern might be defined as 3 Game Rooms. A good guideline is that an enclosed area up to about 20' x 20' should probably count as one Game Room, although this is a guideline only and what actually counts will depend on the site being used. If you have any questions, ask a Marshal whether an area counts as one or more Game Rooms.
This comes into play when casting spells like Ward or Wizard Lock that protect a single structure or room, or when using Area Traps that will affect everyone inside a Game Room. If an area is defined as larger than one Game Room—like the tavern example above that counts as 3 Game Rooms’ worth of size—it will require more traps to trap or more Wards to Ward.