Radiation fog is a type of fog that occurs due to the cooling of the earth's surface through radiation on a clear and calm night. However, there are some other terms used as synonyms for radiation fog. One of the commonly used synonyms is ground fog. This fog occurs due to cooling and condensation of air over the ground. Another synonym for radiation fog is advection fog, which occurs when warm and moist air passes over a cooler surface. Upslope fog, which occurs when moist air is forced to rise over a hill or mountain is also sometimes used as a synonym for radiation fog. Finally, valley fog is a common term used for radiation fog that typically occurs in low-lying valleys or near water bodies such as a river or a lake.