Dark data is the inactive or unused information that piles up in your...

https://www.bookmark-xray.win/dark-data-is-the-information-organizations-collect-but-don-t-use-often-making

Dark data is the inactive or unused information that piles up in your systems—often 60-80% of stored data. It can increase storage and backup costs and raise ransomware exposure by providing attackers hidden entry points