F

(Metric) As a lower-case prefix, f-, see femto-, e.g. fg = femtogram.

length As f, foot in such constructs as f.p.s. system.

physics As F, see Faraday constant.

electromagnetics As F, see farad; see SI alphabet for prefixes.

informatics In hexadecimal notation as F for 15, the 6th digit after 9. Since this is the highest digit in hexadecimal, a string of F's represents a string (four times as long) of binary 1's, and hence a maximal absolute value in a given context.