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

https://www.active-bookmarks.win/dark-data-is-the-information-your-organization-collects-but-never-uses-often

Dark data is the inactive or unused information that piles up in your storage—often 55% of all stored data. It wastes money on storage and backup costs and increases risks like ransomware exposure since old files are less likely to be secured