Nintendo Wi-Fi Connection, or WFC, is a service from Nintendo that allows the Nintendo Wii and Nintendo DS games and applications to connect to the Internet. Super Smash Bros. Brawl is one of the many games that can use the WFC to brawl online with friends or with anyone, as well as send some data to other players. While the network still exists and functions, it is now a legacy connection; it has since been superseded by the Nintendo Network for the Wii U and 3DS.
The Wi-Fi Connection is set to be terminated on May 20th 2014. As a result, it will no longer be possible to play Brawl online.
The Nintendo Wi-Fi Connection allows players to play against each other online for the first time in the series. A primary point of this is that it allows players to either play with anyone in the world or with registered friends. The former, With Anyone, allows players to either take part in standard free-for-all battles via Basic Brawl and Team Battle, while the latter allows for slightly more customisation
In addition to allowing for online gaming, Brawl also allows players to send replays, custom stages, and snapshots to other players whom they have registered. An applied use of this was the Smash Service, a free service that sent players a replay, a custom stage, and a snapshot each day; these pieces of data came from submissions of players, and were deleted at the end of the day.