Pack (pk) : A commercial unit specifying the number of items per package. In retail trade, packages containing 4 items (for example) are often described as "4 pack" or "4pk." The symbol pk is also used for the peck (see 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}