Codewars is a community of developers, who are called Code Warriors (or just warriors), that train on improving their development skills. Think of it like a coding dojo - where developers train with each other and help each other get better through practice.
In our dojo, kata are code challenges focused on improving skill and technique. Some train programming fundamentals, while others focus on complex problem solving. Others are puzzles meant to test your creative problem solving, while others are based on real world coding scenarios.
Each kata is crafted for and by the community. The author (or Sensei) who created kata will initially include one or more languages to train in. Other Code Warriors later can "translate" the kata into additional languages.
Ranks are used to indicate progression and difficulty. Code Warriors complete Kata which are assigned a rank, which in turn earns them a higher rank once they complete enough of them. There are two classes of ranks, Kyu and Dan. You begin with Kyu at level 8 and work your way down to level 1. Then you progress to Dan, where you work your way up from level 1 to level 8.
Why the names Kyu and Dan? The terms are borrowed from a system in Japanese martial arts, which is in turn borrowed from the game of Go. Kyu (or Kyū) indicates the number of degrees away from master level (Dan). This is why they count downward. Once you reach master level, we count upward. Black belts in martial arts are Dan level.