A creepypasta originating on 4chan where people can randomly clip out of reality into a world of endless, randomly generated rooms featuring little more than recessed ceiling lights and yellow walls/carpets. The original post also implies that these rooms are not devoid of life, which should be avoided at all costs.
First popularized in 2019, and spread onto Japanese accounts in early 2022. Later became an international meme in the middle of 2022.
Fans have since expanded the concept and formed several communities based on different versions of the Backrooms with different expanded lore.
