Fog is basically a type of low-lying cloud.
The only difference between fog and mist is in their density. Fog reduces visibility to less than 1 km while mist reduces visibility to no less than 1 km.
The foggiest place in the world is the Grand Banks off the island of Newfoundland, this is because this area represents a meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south.
Argentina is the most foggiest country in the world, having more than 200 foggy days per year.
US city Seattle is famous for having many foggy days per year.
In order for fog to be created the difference between temperature and dew point needs to be smaller than 2.5 °C or 4 °F.
In normal conditions fog will appear at a relative humidity near 100%.If the air has a 100% relative humidity this means that it can hold no additional moisture.
Fog can have many different forms, depending on how the cooling that caused the condensation occurred. The forms of fog include Radiation fog, Ground fog, Advection fog, Frontal fog, Freezing fog, etc.
The foggiest area in the United States is Point Reyes, California with around 220 foggy days per year.