What does f stand for?

Fillial

Fraunhofer lines

Flower

Flower are plant structures involved in sexual reproduction. Thus, they are typically comprised of sexual reproductive structures that is androecium and gynoecium in addition to non essential parts such as sepals and petals. And the presence/absence of these structures may be used to describe flowers and flowering plants.

Fat

Solid triester of glycerol and (mostly) saturated fatty acids.

Fatigue

The phenomenon leading to fracture under repeated or fluctuating stresses having maximum value less than the ultimate strength of the material. The phenomenon leading to fracture under repeated or fluctuating stresses whose maximum value is less than the tensile strength of the material. The weakening or deterioration of a material occurring when a repetitious or continuous application of stress causes strain which can lead to failure.

Flux

Lines of magnetic force moving through a magnetic field. Also, material used to join two pieces of metal being soldered or brazed OR A slag-making ingredient or the increased fluidity of slag. OR Generally refers to a magnetic line of force but may also describe an electric line of force.

fiber(s)

Freeze Compressed File

Fuel

Any material substance that can be consumed to supply heat or power. Included are petroleum, coal, and natural gas (the fossil fuels), and other consumable materials, such as uranium, biomass, and hydrogen. Any substance which is used for producing heat energy, either by means of the release of its chemical energy by combustion or its nuclear energy by nuclear fission.

Femto

Femto- (symbol f) is a unit prefix in the metric system denoting a factor of 0.000000000000001. Adopted by the 11th General Conference on Weights and Measures, it was added in 1964 to the SI. It is derived from the Danish word femten, meaning "fifteen".