Boot loader can mean a disc that is used to defeat anti-piracy
measures on a video game console.
Modern video game consoles are programmed to only load discs that are commercially produced and licensed. If you wish to execute code that you or someone else wrote that isn't licensed, you need a disc that gets past that protection, and allows you to swap in your homebrew game or program.
One example of a console boot loader is the Utopia Boot Disc, which is was released by the Utopia warez group to allow copied or homebrewed Dreamcast games and programs to run.