Homebrew applications are applications, often games, developed by hobbyists to run on game platforms (or mobile phones). Wii had already some homebrew applications using a hack so called Twilight hack. Now, it is even more convenient. There is an application that can be loaded as a Wii channel. In other words, through the Homebrew channel, user can play games (or other applications) that were developed and distributed without the authorization of Nintendo. The games can be loaded through SD cards, and even remotely through TCP!
They are extremely well organized with even a Wiki at Wiibrew.org