Fog in a dream signifies something that is unclear or unknown. This is one of the most popular interpretations for this element in a dream. Fog can also represent confusion, or a lack of clarity about something.
For example, one has been struggling with a decision for so long that it seems impossible to make one way or another decision on it where the foggy nature of this situation persists because there is no foreseeable end to it anytime soon.
When fog is present in your dream, it might also indicate an act of sabotage to your plans, problems at work, depression, confusion, difficulties with relationships and much more.