Flexicocking – continuation of fluid cocking by burning coke into a cock-like low-calorie gas, without a catalyst.

Fluid - (liquid), common term for liquids and gases.      

Fluid catalytic cracking (FCC) – cracking of hydrocarbons in the liquid layer of the catalyst.

Fossil fuels- coal, petroleum and natural gas.

Fraction distillation - distillation process which results in several ingredients (components, fractions) by cooling vapours at specific temperatures.

Fuel oils – products resulting from crude oil refining which are separated at 370–420 ^oC. Used as fuel for thermal electric power plants, heating plants, cement plants and big ship engines