A metric prefix meaning 10-6 (one millionth). The prefix comes from the Greek prefix mikro-, meaning small. In print the prefix is sometimes abbreviated mc- or u- when the Greek letter mu (µ) is not available
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}