the specific percentage of total industry sales of a particular product achieved by a single company in a given period of time.
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British Dictionary definitions for market share
the percentage of a total market, in terms of either value or volume, accounted for by the sales of a specific brand
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012