A sequel to the first game and a prequel to the second game = pre-sequel. Playable claptrap and we finally get an ice element!
Borderlands: The Pre-Sequel takes place between the first and second games in the series. Witness Handsome Jack's rise to power as you play as Athena, Wilhelm, The Sheriff, or Claptrap.
So it looks like Borderlands is not immune to the "ship it off to another studio for a quick follow up while you work on the next-next version" disease. Obviously I'm not a fan of this, but the stuff in the video looks alright and it's on PC so it's next-gen for me. No love for PS4/XBone users is a surprise though.
The game will be released "later" in 2014.