Unsigned code
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In the video game console business, all console games have to be signed with the code designed by the console maker or the game won't load on the console. Each code is different, PS2 uses a different signed code then the XBOX, et al. Unsigned Code refers to a application which doesn't contain the code required for it to load on a console which means that the load unsigned code, you need a modchip, swap trick or exploit.
Without a modchip, swap trick, exploit, et al, unsigned code will not work. For example, homebrew XBOX programs are unsigned code so a modchipped XBOX or a XBOX running a softmod is needed to run homebrew XBOX programs.