Dark data is the inactive or unused information that sits in your storage—often...

https://www.last-bookmarks.win/dark-data-is-the-inactive-or-unused-information-that-piles-up-in-your-storage

Dark data is the inactive or unused information that sits in your storage—often 55% of all stored data. It not only wastes resources, driving up storage and backup costs, but also increases risks like ransomware attacks or data breaches