What is Market Share?

Legal Definition
Market share is the percentage of a market (defined in terms of either units sold or revenue) accounted for by a specific entity. In a survey of nearly 200 senior marketing managers, 67% responded that they found the "dollar market share" metric very useful, while 61% found "unit market share" very useful
-- Wikipedia
Legal Definition
Market share is the percentage of a market (defined in terms of either units or revenue) accounted for by a specific entity. In a survey of nearly 200 senior marketing managers, 67% responded that they found the "dollar market share" metric very useful, while 61% found "unit market share" very useful.

"Marketers need to be able to translate and incorporate sales targets into market share because this will demonstrate whether forecasts are to be attained by growing with the market or by capturing share from competitors. The latter will almost always be more difficult to achieve. Market share is closely monitored for signs of change in the competitive landscape, and it frequently drives strategic or tactical action."

Increasing market share is one of the most important objectives of business. The main advantage of using market share as a measure of business performance is that it is less dependent upon macroenvironmental variables such as the state of the economy or changes in tax policy. However, increasing market share may be dangerous for makers of fungible hazardous products, particularly products sold into the United States market, where they may be subject to market share liability.
-- Wikipedia
Legal Definition
A brand, product, or company in a market it dominates, shown by total sales volume as a percentage of overall sales.