market leader 
noun
1The company selling the largest quantity of a particular product: we have emerged as the clear market leader in the pet retail trade...
- Car market leader Maruti sold 49, 399 units including 5,458 units in exports this October.
- The company has very strong management and is the clear market leader.
- By 1998 we had 200 employed in Dublin and Cork and were the clear market leader in the sector in which we operated.
1.1A product which outsells its competitors: the company made its disposable razor the market leader...
- The product is a market leader but facing heavy competition from several ‘me too’ products or generic drugs.
- Between six and ten in the evening it is the market leader among 15 to 24-year-old Dubliners.