WiiConnect24 is the name of the former online service for the Wii. The system was connected to the internet 24 hours a day, thus the name. The reason for that is so even when the console is off, the console can still transfer data through WiiConnect24. For example, a player's friends can visit your town in Animal Crossing: City Folk even while they're not playing your game. Or, they could download new maps and characters overnight while they're not playing.
WiiConnect24, like Nintendo Wi-Fi Connection uses friend codes, but instead of one friend code per game, it's one friend code per console. Players were able to download Nintendo DS demos through WiiConnect24 and play them on their DS. The service was shut down on June 28, 2013 globally.  Even after all the WiiConnect24 services were discontinued, WFC continued until it shut down on May 20, 2014.
Games Using WC24
This is a list of games that used WiiConnect24.
- Battalion Wars II
- Elebits (the first game to use this service)
- Super Mario Strikers Charged
- Super Smash Bros. Brawl
- Mario Kart Wii
- Animal Crossing: City Folk
- While WiiConnect24 was officially discontinued on June 28, 2013, a homebrew service known as RiiConnect24 was unofficially released in 2015, allowing the user to transfer data. The News Channel, Forecast Channel, Check Mii Out Channel, Everybody Votes Channel, Digicam Print Channel, and Nintendo Channel all required WiiConnect24 to function, although the functionality of all those channels (except for the Digicam Print Channel) would be restored gradually starting in November 2017, with the News Channel, the Forecast Channel, and the Everybody Votes Channel the first three channels to be rereleased for use with RiiConnect24.
-  Ars Technica - Shutdown of Wii's online services