Noclip
To pass through walls or floors that would normally block a player in a game. In Backrooms stories, it means slipping out of ordinary reality.
Context
Games ordinarily use collision boundaries to keep characters from moving through solid objects. A noclip mode lets a player move past those boundaries, and a collision glitch can sometimes have a similar effect.
The original Backrooms story imagines that ordinary reality has boundaries someone could cross in much the same way.