The term PRINTING UNIT is composed of two crossword solutions, REAM (4 letters) and EM (2 letters). A REAM is a unit of paper measurement that is equal to 500 sheets of paper. An EM is a unit of measurement used in typography that is equal to the width of the letter 'M' in a particular typeface. Together, these two terms refer to the unit of measurement used in printing, which is the combination of 500 sheets of paper and the width of the letter 'M'.