Jackson X Series

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 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.