Dark data is the information your business collects but never uses, often...

https://wiki-site.win/index.php/What_Should_I_Do_with_Former_Employee_Folders_on_the_File_Server%3F

Dark data is the information your business collects but never uses, often making up 55% of stored data. It creates storage and backup costs that can reach millions annually and increases ransomware and breach risks by expanding your attack surface