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

https://garrettsbestblogs.theglensecret.com/is-dark-data-ever-worth-monetizing-or-should-i-just-delete-it

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