The full form of F is Fahrenheit

The Fahrenheit scale (/ˈfærənhaɪt/ or /ˈfɑːrənhaɪt/) is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his scale exist, but the original paper suggests the lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from a mixture of water, ice, and ammonium chloride (a salt). The other limit established was his best estimate of the average human body temperature, originally set at 90 °F, then 96 °F (about 2.6 °F less than the modern value due to a later redefinition of the scale). However, he noted a middle point of 32 °F, to be set to the temperature of ice water.

The Fahrenheit scale is now usually defined by two fixed points with a 180 °F separation: the temperature at which pure water freezes is defined as 32 °F and the boiling point of water is defined to be 212 °F, both at sea level and under standard atmospheric pressure.