big four

Any group of four major or largest corporations in a given industry, especially when such a small group has oligopoly or near-oligopoly.

(finance, business, technology) The four largest corporations of Big Tech during the 2000s–2020s, usually defined as Alphabet (f.k.a. Google), Meta (f.k.a. Facebook), Amazon, and Apple.

(business, accounting) The four largest global auditing firms, comprising Deloitte, Ernst & Young (EY), KPMG, and PwC.

(finance) The four largest banks in any of various countries, or (internationally) the Federal Reserve, People's Bank of China, Bank of Japan, and European Central Bank.

(fashion) The clothing trade shows (“fashion weeks”) in Paris, London, New York, and Milan.

(music) A jazz rhythm derived from the marching band beat.

A group of four entrepreneurs who formed the Central Pacific Railroad.

(historical) The four top Allied powers of World War I and their leaders: David Lloyd George of Britain, Georges Clemenceau of France, Vittorio Emanuele Orlando of Italy and Woodrow Wilson of the United States, who met at the Paris Peace Conference in 1919 at Versailles.

(UK, historical) The four largest railway companies in the United Kingdom in the period 1923–1947: the Great Western Railway (GWR); the London, Midland and Scottish Railway (LMS); the London and North Eastern Railway (LNER); and the Southern Railway (SR).