single or dual refers to how many beadlocks are built into the rim. 1 means it only has a ring on the front and the back is normal, 2 has rings on both front and back. Hiper fronts are singles and rears are doubles. the doubles make it tons easier for changing tires and breaking the beads when the time comes.
word of advice, when time to break the bead on the fronts away from the back side, take it to a bike shop with a hydraulic tire machine. I promise, it will take an act of god to break the back bead by hand otherwise.