Gibson "style". He means that it's a rod that acts directly on the wood of the neck, just one length of metal. It's laid into a curved channel and as the bolt at the headstock end it's tightened, the rod tries to straighten, and it corrects the curve of the neck. Another popular style (as used by me at Matt Martin Guitars!) is the box section style which is easier to install and lies directly below the fretboard. Cheers, Matt.