BIS

BIS is an abbreviation meaning "Best In Slot" which is used in videogames (mostly World of Warcraft) that identifies something in the game as "the best you can have at the time".

But nobody will understand you if you use this irl...

Tank 1: What is BIS tank trinket for Brewmaster Monk?

Tank 2: It's the Blood Splattered Scale and Heart of Al'ar