Now that you know that "F&F" translates as "fit and finish," you should get some of the practical meaning as well.
The most common F&F isuses include: uneven face grinding; poor edge grinding; horrendously bad sharpening (complete or nearly complete lack of sharpening isn't an issue for Japanese knives -- that's just how some of them come); grind marks anywhere on the knife, lack of polishing, bent or broken tips (usually happens during shipping -- a partial result of bad packaging -- maybe not F&F but still QC); poorly fitting, or loose bolster; crack in the bolster weld; loose handle or handle scales; poorly fitting and/or fitted handle or handle scales.
High end "German" (includes some Swiss, American, etc., as well) knives seldom have F&F issues. Unfortunately, that's not quite as universally true among Japanese knives -- even expensive ones -- especially for those which aren't manufactured with an eye towards western markets.
It's an overgeneralization, but still useful to think of the Japanese "better knife" market in terms of specialty resellers who will stand as middlemen between the customer and manufacturer, and solve any F&F or other QC problems to the customer's satisfaction; and also to note that Japanese consumers of "better" knives have different expectations.
Tangentially: I'm loathe to characterize the sorts of Japanese knives we usually talk about as "high end," because the Japanese high end is an entirely different world.
Resellers in the western market, especially e-tailers, even good e-tailers, don't offer that sort of buffer. Even with caring and cooperative e-tailers, a marginal or bad knife can become a matter of weeks of emailing and back and forth shipping to resolve a problem -- if, that is, the seller even accepts the problem as a manufacturer's defect.
For whatever reasons, cultural, mercantile and otherwise, there are issues.
That's why when you read knife reviews and advice (or at least my reviews and advice) you see F&F addressed as something other than a given.
"Good" Japanese knives intended for the western market, especially Global and Shun have reliably, wonderfully, German-good, F&F. MAC's F&F is typically very good, but isn't quite as reliable as Shun's or Global's. But MAC has incredibly good US representation (MAC USA), with an outstanding reputation for quick repair and replacement -- along with a 25 year warranty.