I could be a little off as far as I know it's a type of bridle with and extra peice of leather that goes over the bit. One of the school horse at the barn I ride at has this style. I feel like it helps home pay attention because he has a habit of opening his mouth to avoid contact. I feel like this would be a good investment of your horse avoides contact with the bit. I'm not a fan of harsh bits, this horse just has a simple snaffle bit which works wonderful.
Hope this helps