What is Market share
This is a business share of the market it sells in, which is expressed as a proportion of the market. For example, Vodafone own 60% of the mobile phone market. This means that all its competitors make up only 40% of the market. This means all the people that have a mobile phone, 60% of all customers are with Vodafone.
One of the factors involved is the number of business in that industry. But when markets are large then there will always be big players that dominate the market.