A preliminary question is one of terminology. What, if anything, does the letter 'F' stand for? One plausible answer is that it stands for 'fixation', since among other things the F-statistics can be used to measure the rate at which alleles tend to be 'fixed'. Wright himself in his later writings sometimes refers to F as an 'index of fixation'.
Believe it or not, Fst is one of thos population genetic concepts you've almost certainly encountered no matter your background. Related:On Reading Wright, Notes on Sewall Wright: Path Analysis and Notes on Sewall Wright: the Measurement of Kinship.