A common but non-standard symbol for grams per square meter (g/m2), the metric unit of density for paper and for fabric. Paper density measured in this unit is often called grammage
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}