Tom is right. According to the manual, this jumper is for Vio.
However, I'm wondering if this is actually correct. On my board, setting the jumper to 5% increases the Vcore by 5%. Setting the jumper to 10% also increased the Vcore by 10%, according to both the BIOS & MBM as well as the significant rise in CPU temp. Has anyone else seen this w/ their board?