Abbreviation for "cubic," as in cubic feet or cubic meters. This symbol is forbidden by the SI, but it remains in common use in ordinary English text. The proper symbol for cubic feet is ft3, not cu. ft
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}