"F-spacing" is used to refer to the spacing between the pole-pieces of a pickup (usually this is an issue with humbuckers only). An F-spaced pickup is one in which the pole-pieces are set slightly farther apart to accommodate the differences in inter-string spacing associated with having a tremolo bridge, typically found on a Strat-type guitar.

What does the "F" stand for? The answer to this question is somewhat unclear. Some people have said it is short for Fender, while others believe it to stand for Floyd Rose. Seymour Duncan uses the term "Trem-bucker" instead. Some modern tremolo bridges also have standard "non F" spacing.