Homebrew, when used in video games, are games or mods produced by hobbyists for video game consoles which are not intended to be changed to the extent homebrew gives. Official documentation is often only available to licensed developers. Many consoles have hardware restrictions to prevent homebrew, or have system updates to patch out exploits that allow homebrew.
The Wii, along with many other consoles was a big target for homebrew. The Wii was originally hacked by a custom serial port interface.[1]