It is a segregated partition that hold the files needed to restore your computer. It can allow you to reinstall to a clean state (wiping out all your files and making your computer like "new" again) or in more modern cases restore your OS and retain files. It should be a write protected area that you don't read from or write to when operating inside the OS on a day to day basis.
Tampering with your Recovery Partition is definitely for advanced users.
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