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

https://www.pfdbookmark.win/dark-data-is-the-information-companies-collect-and-store-but-never-use-often

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