The share of a market held by a particular firm. The size of this depends largely on the definition of the market: a firm with a small share of a market broadly defined in geographical and industrial terms may have a much larger share of its local market, or the market for a more narrowly defined type of product. This point may be important if monopoly legislation uses market share as a basis for decisions. For example, reference to the Competition and Markets Authority in the UK depends on market share.