weather term
Fog
A cloud that forms at ground level, reducing visibility to less than roughly one kilometre.
Fog forms when air near the ground cools to its dew point, or when moisture is added to the air faster than it can be dispersed. Radiation fog, the most common type, forms on clear, calm nights as the ground cools rapidly and chills the air just above it, and typically clears within a few hours of sunrise as the sun warms the ground back up.