The term "Fog" usually refers to the narrative structure. In these stories, the protagonists often wake up with no memory, find themselves in a strange village with arcane rules, or are trapped in a "copy" (a dungeon-like scenario) where the objective is unclear. The world-building is intentionally disorienting.
Unveiling the Magic of FOG [e-sports] : A Deep Dive into the Beloved Danmei Novel fog danmei