What is a Floyd Rose?

Floyd Rose is an inventor who designed the famous Floyd Rose locking tremolo unit. The Floyd Rose tremolo 'locks' the strings in place both at the bridge and at the headstock via a specially designed nut. This allows the player to make a whole range of extreme whammy bar noises. It allows the strings to be depressed until slack before returning to perfect tune when the whammy bar is released.

Jackson X series guitars have a 'compound radius' fingerboard. What is this?

The radius of a fingerboard is, in layman's terms, how curved of flat it is. Vintage guitars have more curved fingerboard (hence a lower nummber value like 7.25""). More modern instruments tend to have flatter radius fingerboards with higher values like 12" and 14". A compound radius is a radius that gets progressively flatter as the frets ascend. In the case of Jackson, the lowest fret at the nut have a 12" radius, which flattens out gradually along the neck until the 24th fret, which is 16" in radius. The idea is that you get a slight curve in the radius down where you play a lot of chords, and an extra flat radius where you tend to play most of your solos.

Jackson make two different 'flying V' guitars: which is which?

Jackson make two separate V guitars but neither is a 'Flying V' since that is a Gibson trademark. Jackson's V shaped guitars are the King V and the Randy Rhoads. The King V is more symmetrical in terms of its body shape. The Rhoads (often referred to as the RR) has an asymmetrical design with one 'fin' significantly longer than the other.