In the context of travel, insurance, and law, fog is generally classified as a "force majeure" event (an "Act of God"). Force majeure refers to unforeseeable, extraordinary circumstances beyond the control of the parties involved that make it impossible to fulfill a contract. Because fog is a natural atmospheric condition that can make it unsafe for pilots to land or take off and for ships to navigate narrow channels, it falls squarely into this category. When a flight is delayed or canceled due to fog, the airline is usually not legally required to provide financial compensation (such as the payouts required under EU 261/2004) because the delay was caused by weather, not by the airline's own technical or staffing issues. However, the airline is still responsible for its "duty of care," which typically includes providing food vouchers, communication access, and overnight accommodation if the fog persists. For travelers with "trip cancellation" insurance, fog-related delays are usually covered, allowing you to recoup costs for missed tours or non-refundable hotel stays. It is always a good idea to get a written statement from the airline or port authority confirming that weather was the cause of the delay to simplify your insurance claim.