Printer's widths are a set of standard measurements used in the printing industry. The two most common measurements are ENS (3 letters) and EMS (3 letters). ENS stands for 'EN' which is a unit of measurement equal to half an inch, while EMS stands for 'EM' which is a unit of measurement equal to the width of a capital letter M. These measurements are used to ensure that printed materials are consistent in size and shape.