Dark data is the unused information stored across your systems, often making up...

https://domgodwinson38.gumroad.com/p/what-should-i-do-with-former-employee-folders-on-the-file-server

Dark data is the unused information stored across your systems, often making up 55% of all data. It matters because it increases storage and backup costs and raises your risk of ransomware attacks or data breaches