Economic Definition of market share. Defined.
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Term market share Definition: The fraction of an industry's total sales accounted for by a single business. In general, market share is a "first-guess" indicator of a firm's market control. If, for example, a company has a market share of 100 percent (that is, a monopoly), then you can rest assured it has a substantial amount of market control. A company with a 25 percent market share has less, but still notable, market control. In fact, when you get right down to the bottom line, the phrase "market share" is only worth mentioning for oligopolistic firms with a significant degree of market control. There really is no market control for a monopolistically competitive firm with a 0.00000001 percent market share.