Some popular games have implemented an "always online" requirement where you will need to be connected to the Internet to play the game. There are some benefits to this from the viewpoint of the developers, but most players find it to be a very inconvenient feature. There were some rumors that Boderlands 3 requires an always on connection, but is this even real?
Luckily for us gamers, there is false, and you can play Borderlands 3 offline. You will obviously not be able to play with your friends, but other than that, the entire game should be exactly the same independently of it you play online or offline.