Thick fog
A dense, low cloud at ground level — visibility lost not to darkness but to suspended water.
Thick fog in a dream is the dream's image of visibility lost not to darkness but to suspended water. The day is technically lit; you still cannot see. The dream brings thick fog when something in your life — a decision, a relationship, an emotional state — is happening in conditions where the input is present and unreadable. A fog waited out at a known stopping point is the dream affirming that the right response is to stay still. A fog walked into with confident pace is the dream noting that you are moving on memory of the path, and the memory is no longer reliable as a guide.