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

https://www.blaze-bookmarks.win/dark-data-refers-to-the-55-of-stored-information-that-organizations-collect

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