Backrooms

Coined by an anonymous 4chan user on May 13, 2019:

If you're not careful and you noclip out of reality in the wrong areas, you'll end up in the Backrooms, where it's nothing but the stink of old moist carpet, the madness of mono-yellow, the endless background noise of fluorescent lights at maximum hum-buzz, and approximately six hundred million square miles of randomly segmented empty rooms to be trapped in
God save you if you hear something wandering around nearby, because it sure as hell has heard you

the Backrooms

1. (Internet slang) An online urban legend or creepypasta of a seemingly endless maze of empty hallways, often described as being inhabited by monsters or having multiple levels or floors.
   • 2022 March 29, Andrew Lloyd, “The Backrooms: How a Creepy Office Photo Became an Internet Bogeyman”, in VICE‎, archived from the original on 2023-05-07:

     Threads are filled with talk of new levels that could sit above, below or beside the Backrooms, including pitch black tunnels and an abandoned hotel. These fan-made spaces have their own design and background stories, but they've caused a split in the community.

• The Backrooms on Wikipedia.Wikipedia