How is it that everyone that I talk to, knows what I am talking about when I say those words, but apparently you don't?
So it would be Google, Microsoft, Facebook, Amazon, Apple, and maybe Netflix depending on who you ask.
And yes, I know that is more than 5 companies. It is a shorthand for "those prestigious, large tech companies that new grads apply to, and hire lots of people, and have large market caps".
If I talk to any new grad who is applying to companies these day, they will know what I mean when I say "big 5 tech companies".
This is a very common term in the interview/tech market and discussions.
The fact that this is how people use these words, makes it the definition.
Lots of people in the real world know exactly what it means when people say "big 5 tech companies".
You'd have to be extremely obtuse to not know what people mean when they say those words.
* Admittedly would swap Netflix with Microsoft in the FAANG acronym.