A symbol for international standard paper sizes, followed by the size number, as in C4. The C series of sizes is used primarily for envelopes. A table of sizes is provided
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}