what is the London system?

And most top players also play London on a regular basis.

He plays all sorts of openings to catch his opponents off guard. Also, it’s a lot different when a super-GM plays a opening than some 1500 who plays the same opening against everything. He’s also played the Berlin and the Exchange Slav but no one goes promoting that or mention how when he plays 1.d4, he most of the time plays the Queens Gambit. Quite clearly he likes the Queens Gambit more if he clearly plays it more

It is funny how openings gain associations. Presumably these are not the same for different people.  For me, I have always thought of the Queen's Gambit (and 1. d4 Nf6 2. c4) as being very "professional" and the London as being "amateur". This is because most of my chess studies were in an era when I virtually only ever saw the London played directly in amateur games, while the Queen's Gambit and the moves above were the sort of thing played in world championship games and pro games as well as in the amateur chess world.

In truth, both are perfectly decent ways to play.

Yeah, Queen's Gambit and Indian Game are the two most popular ways to play d4.

And so is 1. d4 Nf6 2. Bf4. I am with Simon Williams on this one.