The mass of the electron, often used as a unit of mass in particle physics. An electron has a mass of about 9.109 382 x 10-31 kilogram, 9.109 382 x 10-28 gram, or 0.510 9989 million electronvolts (MeV, see next two entries)
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}