The numbers refer to the magnification and the diameter of the objective lenses. For example, in the specification "8x42" for a pair of binoculars, "8x" indicates the magnification, meaning that the viewed object will appear eight times closer than it would to the naked eye. The "42" refers to the diameter of the objective lenses in millimeters, which determines how much light the binoculars can gather for a brighter image.