What does FS mean?

Answer 1

The F clef is another name for the bass clef. The term comes from when the F-clef used to be movable, so the line between the two dots of the F-clef is where the pitch F3 (the F below middle C) would be. Now, since the only F-clef that is used is the bass clef, the terms are now synonymous.

Answer 2

Would depend on the situation, if it's related to mountainbikes it'd mean full suspension, i.e. both front wheels being able to move in relation to the main frame. Other areas are quite likely to mave other meanings for the same letters.