A metric unit of mass equal to 1015 grams or 1 gigatonne (one billion metric tons). This unit is used in atmospheric science and other scientific contexts where large masses are considered
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}