Originally known as the Big Four (or the Big Four Tech Companies). In the last year they added a new one. The GAFAM companies are the five most valuable public corporations in the world as measured by market capitalisation. They can be considered an oligopoly that takes control of the internet. They are:
Read more about them on Wikipedia
Most of the business of those companies are based on the systematic espionage of their users and selling their data to the biggest bidder. The correlation between alleged anticompetitive behavior and questionable online privacy practices is also far from clear. And not only that, they also are known for avoiding taxes all around the world.