An informal abbreviation for million in expressions such as "$500M" for 500 million dollars or "Unemployment Reaches 4M" in a newspaper headline. In binary contexts such as computer memory, M often represents 220 = 1 048 576 (see mebi-, below)
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}