A thick, persistent ground fog, canonically found in parts of California's Central Valley, where it forms from late fall through early spring (rainy season), which may contain cold or freezing drizzle.

plural of ground fog

(weather) A low-lying fog extending only a few feet above ground.

(rail transport, UK) A small explosive charge (detonator) which can be placed on a railway line in fog, to be detonated by a train passing over it as a warning signal to the driver.

plural of fog signal

A readability metric for English writing, estimating how many years of formal education a person needs in order to understand the text on the first reading. It is based on the average sentence length and the proportion of words of three or more syllables.