Means if you set the wrench on a bolt one way, the wrench (box end) will slip all the way over the bolt and to the other side. If you put it on the bolt the other way, it will catch on the bolt not allowing it to pass over it completely. That feature makes it so you don't have to work so hard to keep the box end on the bolt once it starts to raise up some away from what it was tightened against.
These wrenches are 12pt. They are just like the Blue Point set.