Fretboard radius dictates the curvature of the frets. As a general rule of thumb, the tighter the radius (smaller the number), the easier it is to play barre chords and general rhythm guitar. Conversely, this means that the larger the radius and fletter the fretboard, the easier it is for lead guitar.
Tighter radii are generally associated with vintage guitars, and larger radii with modern guitars. Compound radii fretboards are where the radius flattens out towards the higher frets. This gives the best of both worlds; great lead play-ability at the higher frets, without compromising at the lower frets.
10" will be the most familiar if you are unsure. This radius comes as standard with our Semi-Custom guitars.