Typesetter's Units are a unit of measurement used in typesetting and printing. EMS (3 letters) stands for 'em-sized units' and is a unit of measurement equal to the width of the letter 'M' in a particular font. PICAS (5 letters) stands for 'pica-sized units' and is a unit of measurement equal to 12 points, or 1/6 of an inch. Typesetter's Units are used to measure the size of typefaces, line spacing, and other elements of typesetting and printing.