A unit of quantity for paper. An ordinary ream is 480 or 500 sheets; a printer's ream is 516 sheets. The additional amount is to allow for sheets that may be spoiled in shipment. The unit is also called the perfect ream
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}