Definition of big three:
(n) :
Any group of three major or largest corporations in a given industry, especially when such a small group has oligopoly or near-oligopoly.
(n) :
(US) The three major traditional commercial broadcast television networks in the United States: CBS (the Columbia Broadcasting System), NBC (the National Broadcasting Company), and ABC (the American Broadcasting Company)
(n) :
(US) A trio of three major management consultancies: McKinsey & Company, Boston Consulting Group, and Bain & Company.
(n) :
(economics) China, Japan, and Korea, three major Asian economies.
(n) :
(tennis) Novak Djokovic, Roger Federer, and Rafael Nadal, each considered to be among the greatest tennis players of all time.
(n) :
(UK, World War II) The World War II military alliance consisting of the Soviet Union, the United States, and the United Kingdom.