The Nintendo Wi-Fi Connection is a service used for online multiplayer gaming, created and run by Nintendo. It is compatible with Nintendo DS, and Wii games.
Friend Codes
A unique 12 digit code is generated by every game that uses the Nintendo Wi-Fi Connection, once it is loaded in a Nintendo DS or Wii. These codes are denominated Friend Codes, and they can be exchanged with other players and be used to keep friend lists in each game. Friend Codes are unique to a copy of a game, and new Friend Codes can be generated by using a different copy of a game or loading the same copy in a different system.