Smash Stack
Smash Stack is the name for the exploit that allows one to use Super Smash Bros. Brawl's Stage Builder to modify otherwise-protected system memory, allowing the usage of hacks without specialized hardware.
The name of the exploit implies its function. By getting the Wii to load a custom stage file that's bigger than the block of memory reserved to hold it, due to the code not checking to see whether the stage file is too large, a stack smash occurs. Due to the way the exploit works, the subject stage file must be the only custom stage on both the SD card and on the Wii itself (including the default ones and any daily downloads), or the game will likely freeze as it tries to load the stages. Once the game is quit or the console is turned off, all traces of the hack disappear, though the method can be used to install things such as the Homebrew Channel.
Unlike most other Wii hacks involving stack smashes, which tend to involve editing save file data to accomplish a similar effect, the Smash Stack is entirely self-contained within Brawl as it is running. As a result it is not possible for Nintendo to inform Wiis what such a file looks like and delete it if detected, due to the process occuring outside the console's control. This renders the hack particularily resilient compared to the Twilight Hack (involving The Legend of Zelda: Twilight Princess), which was the other major avenue of hacking Wiis via in-game exploits before it was eventually defeated permanently, and is strong enough that even a Wii U running in Wii mode is vulnerable to it (though this doesn't allow hacking of the Wii U itself, only the Wii part). As a result of its unpatchability, simplicity, and presence in a popular game, the Smash Stack is one of the most common ways of hacking or modding a Wii, and the method is supported by all major Brawl mods for players who do not wish to make any permanent changes to their console.
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