Dark data is the inactive or unused information stored across your systems,...

https://www.jelly-bookmarks.win/dark-data-is-the-information-your-organization-collects-but-doesn-t-use-often

Dark data is the inactive or unused information stored across your systems, often making up 55% of all data. It poses a real risk by increasing exposure to ransomware and breaches and drives up storage and backup costs, sometimes wasting millions annually