US Grading

Correct. It means the coin is in the VF range but has been cleaned, scratched, dented, tooled, engraved, etc or even if it has gunk on it or if chemicals have touched the coin and altered it's surface.... the more rare the coin, the more this does not matter but the more common you get the more it will hurt the value. Values can drop anywhere from 10%-80% depending on the rarity and desirability, or lack there of, of the coin

Whatcha got?

Using a Shield nickel as an example you can never go wrong following this pictorial guide from the best:

http://www.pcgs.com/Photograde/#/ShieldNic/Grades

It even shows you the minute differences between VF-20. VF-25, VF-30, and VF-35 etc.

Even though the URL I've provided here includes the words, ' Shield nickel', it still takes the reader to the main page for choosing what particular US coin to grade.

I do have a question though. If an obverse side of a coin matches a VF-35 but its reverse is an F-12, what do numismatists consider the entire grade of the coin?