Mostly when you watch newly arrived game's trailer or game play, it's mentioned with a caption E3.
Actuality E3 (Electronic Entertainment Expo) is a premier event which is most related to video games and products. There is more than 50 gaming and technology companies meet under one Roof.
This video will explain much more about it !!
https://youtu.be/9VSeKRS0YWE
in Sri Lanka