Just means that it the box has been opened and it may not contain all the contents.
Most of the time when I get open box items I just get whats specified. In the case of mobos Usually dont get driver cd sometimes no backplate. But no problem go to site for drivers and call Asus for a new backplate usually it is free for the backplate. I think ECS made me pay a buck or something....Also I have never recieved a bad mother board this way, although others may disagree.