It's one kind of playing style of MAIET's MMO third person shooter, GunZ: The Duel. It consists of abusing and exploring glitches from the game, mainly with the in-game swordplay.
It became so popular, that approximately 85% of GunZ players in the world knows at least the most basic movement of K-Styling, BF (Butterfly).
Players improved with time the Korean Style itself, and lots of new moves appeared. Basic ones, such as SS (Slash Shot) or advanced ones.
Some players keep rumoring that a Korean player named "Korean" invented the Korean-Style, and brought to the international GunZ, where it began to spread over the world.
It's also known as 'K-Style', 'KS' or even 'Korean S.'
¹ That player is a KS!
² He keeps K-Styling, I hate that.
³ Korean Style is a style invented by the player Korean