The percentage of alcohol, by volume, present in a mixture. In winemaking, for example, a 13o wine is 13% alcohol by volume (13% v/v). This unit is also called the degree Gay-Lussac (o GL) after the French chemist Joseph-Louis Gay-Lussac (1778-1850)
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}