A private road means that a part of the land you own is made into a road according to the law, and you cannot build a building or a fence on that part. When the description of the property says "private road burdened," it means that there is a part of the land to be sold that should be burdened as a private road.
Basically, although the private road part is not accessible to others, please note that not all of the land described in the property summary can be used effectively.