This abbreviation can be found for any binoculars that you can buy from us. It specifies the magnification and the size of the binoculars’ objective lens. The first number represents the magnification, in this case therefore it is a magnification of 10x. The second number represents the size of the objective lens, which is always expressed in millimeters. A 10x42 binoculars therefore has a 42mm objective lens.