Printers' Measures are terms used to describe the size of a printed page. ENS stands for Envelope Size, which is the standard size of an envelope. EMS stands for European Metric Size, which is a metric system used in Europe for paper sizes. PICAS stands for Picas and Points, which is a unit of measurement used in typography. NNNN stands for Non-Standard Numbering, which is a system used to identify paper sizes that are not part of the standard paper size system.