雲量
Cloud cover is often referred to as "mist" when encountered on mountains, whereas moisture suspended above a body of water or marsh area is usually called "fog". One difference between mist and fog is visibility. The phenomenon is called fog if the visibility is or less. In the United Kingdom, the definition of fog is visibility less than for driving purposes, UK Highway Code rule 226, while for pilots the distance is 1 km. Otherwise, it is known as mist.